A Glossary of Basic Chess Variant Terms

- A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z -

This is an update to an earlier glossary that John William Brown first put together in the year 2000. It is now 2020, and this revision will aim to:

Weed out terms that are not commonly used.
Add terms that should be in the glossary.
Make sure that terms are defined briefly, cleary and unambiguously.
Make sure that terms are defined consistently with current usage.
Make sure that terms are defined in a manner that works with multiple Chess variants.

A

adjacent: adj. Of two square spaces, sharing a common side or corner.; adj. Of two hexagonal spaces, sharing a common side or having their corners connected by the side of another hexagonal space they each share a side with.; adj. Of two 3D spaces, sharing a common face, edge, or vertex.
alfil: n. (Arabic for 'the elephant') An elemental piece. Leaps over a diagonally adjacent space to the one beyond. Sometimes referred to as a 2-2 leaper.
altitudinal: adj. neologism. In a direction that goes only through the third dimension, which is normally up and down. Available only in 3D and higher dimensional Chess variants.
This is what the word vertical normally means in English, but since that word has been conscripted for the second dimension, this neologism may be used for the third dimension.
angular: adj. In a direction that is not radial.
The Knight is the only piece in Chess with an angular move. Other elemental angular movers include the Camel, the Zebra and the Giraffe.
army: n. All of the pieces belonging to a given player.
array: n. Another word for initial setup
attack: 1. n. The threat of capture of a piece on its current space, on a space it may move to, on a space it may pass through while making a move, or on an intervening space while making a leap.
The first two types of attacks are common in most Chess variants, including Chess, Shatranj, Xiangqi, and Shogi. The third comes into play in Chess when a pawn may be captured en passant or when the king is not allowed to move through check when castling. Other examples of it may be found in Caïssa Britannia, whose royal queen may not move through check, and in Fusion Chess, which also has royal pieces incapable of moving through check. The fourth is found in Metamachy, which allows the king to leap two spaces on its first move, though not over checked spaces, and it is illustrated in Fusion Chess, whose cavalier king may leap as a knight but not through check.; 2. v. To threaten a piece with capture in any manner described above.; 3. v. colloquial. To make a move that creates a new attack on an enemy piece on its current space.
attacked, under attack: adj. Subject to attack; threatened with capture.
Zillions-of-Games has an attacked? function. This can be used in move definitions to indicate whether a piece at its current position, which may be its starting position, a position on the move, or its final destination, can be captured by an enemy piece there. Programming Fusion Chess revealed one limitation in how this works. In that game, some royal pieces cannot move through check, and attacked pieces are not allowed to split apart. Even when the long-range move of a royal piece was illegal due to being unable to complete it without passing through check, its attack on a non-royal piece would still register. So, Zillions was using a pseudo-legal version of attacked that avoided excess calculation by assuming the attack from the long-range royal piece was legal instead of checking whether attacks from other pieces hindered its ability to attack. Fusion Chess was then modified to use this interpretation of attacked.
augmented piece: n. A familiar piece that has been given additional powers of movement.

B

bare King

n. A King that remains after all friendly pieces have been captured.

bare King rule

1. n. In Orthodox Chess, a draw may be claimed when (1) one's King is bared and (2) each player has made 50 consecutive non-Pawn moves without making a capture.

2. n. In some historical variants, a bare King loses the game. This is sometimes paired with the additional rule that if a newly bared King immediately bares the enemy King, the game becomes a draw.

board

n. The playing area of a Chess variant, which is normally composed of interconnected spaces that pieces may move between using different powers of movement. Historically, boards have been physical artifacts, but thanks to computers, boards may also be graphical representations or mathematical models.

board move

n. Any move that does not introduce a new piece to the board. (Compare drop.)

C

Camel: n. An elemental piece. A 3-1 leaper.
capture: v. To legally remove an enemy piece from the board.
In Chess and many other variants, this removes it from the game entirely. In some other variants, a captured piece may be returned through play. For example, Grand Chess allows promotion only to captured pieces, Shogi allows players to take possession of captured pieces and play them as their own, and Hostage Chess allows exchanges of captured pieces.
capture by displacement: v. To perform a displacement capture.
capture custodially: v. To perform a custodial capture.
capture in passing: 1. v. To capture an enemy piece prior to completing a move.; 2. n. The act of capturing an enemy piece prior to completing a move.
capture move: n. A move to a square that is necessarily occupied by an enemy piece, which is captured. (Compare passive move.)
capturing move: n. A move that is capable of capturing an enemy piece on a certain space should there be one there.; n. A move that does in fact capture a piece.
capture square: n. For a given piece, a square that may be entered only to make a capture. [e.g.: The Pawn's forward-diagonal squares.] (Compare passive square.)
castling: n. An Orthodox Chess rule that serves to secure the King by moving it to the far side of either Rook. This rule has been adapted to chess variants in a variety of ways, described in more detail on the Castling page.
cell: n. A cubic space on a 3D board. (Dickins); n. An alternate word for space.
check: n.An attack on a royal piece.
Chess and many other variants do not allow the royal piece to be captured, and without that possibility, check might be thought of as a mock attack. Be that as it may, it still has the full force of a real attack. The royal piece must still respond to check as though the threat of capture were real. When Chess and similar variants are programmed, the threat of check is treated just like the threat of capture, the only difference being that the game ends before the royal piece can be captured.; v.To threaten a royal piece with check.
checked: adj. Of a royal piece, being attacked
checkmate: A position in which a royal piece is checked, and the player has no legal move that can end the check.
checker piece: n. (See overtaker.)
Chess: 1. n. Orthodox Chess; 2. n. The Platonic form, class, or family of games that Orthodox Chess is a specimin of. See What is a Chess Variant?.
chess board: n. The 8x8 grid that Chess is played on.; n. Any board that any Chess variant is played on.
chessman: n. Another name for a chess piece.
chess piece: 1. n. An abstract entity employed in a chess game as a nexus point for various assigned powers of movement.; 2. n. A physical object or graphic image used to represent a chess piece.
chess variant: n. A game sufficiently similar to Chess. The ones we know of are typically inspired by or related to Orthodox Chess, but since similarity is the main criterion, there could be some that have been independently invented. See What is a Chess Variant? for more details.
citadels: n. A space or area that functions something like an immobile royal piece. (Compare palace.)
In Tamerlane chess, for example, the game is won if a player moves his king into his opponent's citadel.
colorbound: adj. Describes a piece whose powers of movement would never allow it to reach spaces of the other color on a checkered board. The Chess Bishop is the best-known example of a colorbound piece. Other examples include the Ferz, Dabbaba, Alfil, and Camel.
column: n. A complete altitudinal row of spaces on a 3-D board. (See rank and file.)
combined piece: n. Another name for a compound piece.
compound piece: n. A new piece created by combining the powers of movement of existing pieces.
control: v. To be able to capture an enemy piece that happens to move to a given space, making it disadvantageous for the opponent to move there.
coordinal plane: n. Within a 3-D board, any plane which lies parallel to two axes and, necessarily, lies perpendicular to the third. (x & y, x & z or y & z)
crowned: adj. Having the additional move of a King. The use of this term does not mean that it has become a royal piece.
custodial capture: n. A type of capture that is made by flanking an enemy piece with two friendly pieces which complete a straight line of three adjacent squares.
CVPhile: n. An unused name for one who frequents the Chess Variants Pages.
cylindrical chess: n. Chess played on a board that is rolled into a cylinder, allowing either its two outer ranks or its two outer files to be joined. Movement around the board is thus continuous, as the the board's axial borders are now eliminated. (Typically played on a flat board with the wraparound rule.)

D

Dabbaba: n. (Arabic for 'war machine') An elemental piece. Leaps over an orthogonally adjacent square to the square beyond. Sometimes referred to as a 2-0 leaper.
defend: v. To cover a friendly piece with a capturing move, such that an enemy piece that captures it may be captured back, making it disadvantageous for the opponent to capture it.
development: n. The coordinated movement of chess pieces toward board positions that are intended to further tactical or strategic goals.
diagonal: adj. In a direction that changes in two dimensions in equal measure on a board whose spaces are right-angled.
On a 2D board, changes of (1,1), (1,-1), and (2,2) are all examples of diagonal movement. On a 3D board, (1,1,0), (1,0,1) and (0,1,1) are all examples of diagonal movement. This is not to be confused with 3D diagonal, which is movement through three dimensions in equal measure.; In a direction that passes through the opposite corners of a polygonal space, or through the opposite edges of a polyhedral space.
This is a broader definition that works for hexagonal boards and still works for right-angled boards. Since a hexgonal board has three axes on a two-dimensional plane, it uses only two of them for coordinates. Thus, movement along diagonals does not always change each coodinate in equal measure.
diagonally adjacent: n. Of two spaces, sharing a common corner on a 2D board, or a common edge on a 3D board. (Compare orthogonally adjacent.)
displacement capture: n. A means of capture whereby the capturing piece moves to an enemy-occupied square and removes the enemy piece from the board.
distant: adj. Of two spaces, not being adjacent.
divergent: adj. Of a piece, having different powers of movement for capturing moves and non-capturing moves. The Chess Pawn and the Xiangqi Cannon are two common examples of divergent pieces.
drop: 1. v. To place a captive or reserve piece on the board to subsequently be used as one's own. (Compare board move.) 2. n. A captive or reserve piece that may be placed on the board to subsequently be used as one's own.
drop piece: n. (See reserve piece.)
drop zone: n. For certain shogi games, an area of the board where drops are allowed.

E

elemental piece

n. A chess piece whose powers of movement consist in being able to make a leap of a single specified distance in any direction it is possible to make a leap of that distance.

On a 2D board, the distance is specified by an unordered set of two integers, indicating how many ranks and files away the leap is, and these two integers are used in both orders. A Wazir, for example, is a 1-0 leaper. Note that this is the same as a 0-1 leaper. It may leap one file and zero ranks away, or it may leap one rank and zero files away. In 3D games, elemental pieces would be defined by three integers, and the usual 2D elemental pieces would be adapted to 3D chess by adding zero to the two integers already defining them. In general, the number of integers defining a distance will match the number of dimensions the game is played on. For hexagonal games, the same ideas would be applied visually rather than in terms of the coordinate system.

The following are other examples of elemental pieces:

the Ferz is a 1-1 leaper.
the Dabbaba is a 2-0 leaper.
the Alfil is a 2-2 leaper.
the Knight is a 2-1 leaper.
the Camel is a 3-1 leaper.
the Zebra is a 3-2 leaper.
and the Giraffe is a 4-1 leaper.

endgame

n. The last stage of the game wherein there are relative few pieces remaining on the board. The primary concern of the endgame is to subdue and checkmate the opponent King.

enemy piece

n. Any piece belonging to a given player's opponent. (Compare friendly piece.)

en passant capture

n. An Orthodox Chess rule than can be adapted to chess variants as follows: A Pawn making an initial multi-square advance may be captured by an enemy Pawn, if the advancing Pawn passes through a square that is guarded by the enemy Pawn. To capture, the enemy Pawn moves forward diagonally to the vacant passed-though square and removes the advanced Pawn from the board.

en prise

adj. Of a piece, being under attack in such a way that its capture could not be compensated for. For example, if it were left undefended, allowing an enemy piece to capture it without being captured back.

exchange

n. Consecutive captures whereby each player wins material.

F

fairy chess: n. A system of alternate pieces, boards and rule variations popularized by British chess columnist T. R. Dawson in the second quarter of the 20th Century. The system was initially used to compose chess problems and eventually became the foundation of the heterodox chess movement.
Ferz: n. (Arabic for general) An elemental piece. Moves to a diagonally adjacent square.
FIDE Chess: n. Chess as codified by The Fédération Internationale des Échecs. Another name for Orthodox Chess.
file: n. A complete vertical row of spaces on a board. The first part of a coordinate normally designate the file. (Compare rank.)
finite mover: n. A piece that cannot move beyond a fixed distance from its current position, regardless of board size, overall board position, or the availability of empty spaces. [e.g.: The Knight, the King, the Pawn.] (Compare infinite mover.)
flip piece: n. A heraldic piece displaying different identity symbols on each side. The piece may be flipped over at the close of a move (or as a move in itself), and assume its alternate identity.
forward: adj. In a direction that goes toward the spaces furthest from the player's own side of the board. (Compare rearward.)
free castling: n. A rule variation that allows more leeway in castling: (1) the King moves outward to any square up to and including the Rook's home square; (2) the Rook moves inward to any square up to and including the King's home square.
friendly piece: n. Any piece belonging to the player in question. (Compare enemy piece.)
funny notation: n. A simple notational system, created by Ralph Betza, for describing the powers of movement of chess pieces. (See Betza's funny notation.)

G

Giraffe: n. An elemental piece. A 4-1 leaper.
great chess: 1. n. A term used in the Middle Ages to describe a number of large chess variants.; 2. n. A modern variant created as a tribute to one of the large variants of the Middle Ages.
guard: v. (See defend.)

H

hand: n. One's cache of reserve pieces. (Such pieces are said to be "in hand.")
heraldic piece: n. A flat shield-like or wedge-shaped chess piece that displays a move diagram or an identifying symbol on its face. Shogi pieces are an example of this.
heterodox chess: n. A term sometimes used to denote chess games other than Orthodox Chess.
hex: n. A six-sided space of a hexagonal chess board.
hexagonal: 1. adj. Of a board, being composed of spaces in the form of interlocking, regular hexagons. A regular hexagon is both equilateral and equiangular and so perfectly symmetrical.; 2. adj. Of a variant, being played on a hexagonal board. The moves of the pieces are amended accordingly.
home square: n. The square that a given piece occupies in the initial array.
hop: v. To move as a rider except that a single intervening piece, known as a screen, is passed over.
hopper: n. A type of piece that moves by hopping.
The Cannon from Xiangqi is the most widely known hopper, but it is actually a divergent piece that hops to capture. The Cannon from Janggi is a true hopper, though it has the added restrictions that it cannot capture or hop over another Cannon.
horizontal: adj. In a direction that goes only along the first dimension, which is left and right (or figuratively east and west) on a chess board composed of square spaces. (Compare vertical.)
In normal algebraic notation, the first part of a coordinate is a letter referring to a file. A move that changes only the file, such as a1 to h1, moves through the first dimension.

I

in hand: n. (See hand.)
initial position: n. (See home square.)
initial setup: n. The initial arrangement of pieces on a chess board.
intersection: A variation of the square space, common to some oriental variants in which pieces are placed on the intersections of lines instead of within enclosed squares. This is normally a difference only in appearance, though some games have been played on both enclosed squares and the intersections of the lines forming those same squares.
intervening piece: n. A piece residing on an intervening square.
intervening: adj. Of a space, lying on the shortest path between two other spaces.; adj. Of a space, lying on a path that a particular piece may take from one space to another.; adj. Of a piece, lying on an intervening space.
infinite mover: n. A piece that has no natural limit to the distance that it can move from its current position. This limit is determined solely by (1) board size, (2) board position and (3) the availability of empty spaces. On an 'infinite board', with no intervening pieces, an infinite mover could theoretically move on forever. (e.g.: The Bishop, the Rook, the Queen, any rider.) [Compare finite mover.]

J

jump: v. To leap to a distant space.
While every piece in Chess can leap at least one space, the Knight is the only piece that can leap further than that. So, it's common for descriptions of the Knight's move to say that it jumps. Unlike leap, jump is not used as a technical term for describing one-space moves.

K

King's leap: n. A rule variation that allows a King to make a once-per-game leap, the nature of which is prescribed by the rules of the game.
Knight: n. An elemental piece. A 2-1 leaper.

palace: n. An area of the board, usually paired with one at the opposite end of the board, wherein the royal piece and certain other pieces are confined, and sometimes wherein different rules apply. (Compare citadel.)
In Xiangqi and Janggi, the General and two Guards are confined to 3x3 palaces on opposite sides of the board. In Janggi, pieces get to move along the diagonal lines of the palace.
pass: v. To voluntarily forfeit one's turn.
passive: adj. Non-capturing.
passive move: n. A move that may not be performed concurrently with a capture. (Compare capture move.)
pass-through square: n. For certain line pieces, a square that must be passed through in order to proceed to subsequent squares. A piece may neither stop nor capture on a pass-through square. [e.g.: The first diagonal square of the xiangqi Elephant's move.]
perimeter: n. A locus of spaces lying equidistant from the same space.
The first perimeter consists of all adjacent spaces. The second permeter consists of all non-adjacent spaces that are adjacent to the adjacent spaces. Each higher perimeter consists of all the spaces adjacent to those in the next lowest perimeter that are not in any lower perimeters.
piece: n. (See chess piece.)
piececlopedia: n. A CV Page describing a number of chess variant pieces. (See Piececlopedia.)
point: n. Another name for intersection.
position: 1. n. A piece's location on a chess board in terms of what space it is on.; 2. n. The collective locations of all chess pieces on the board.
postal chess: n. Chess played by mail whereby each player posts a single move per mailing. Postal chess was popular throughout most of the 20th Century, but is now being supplanted by online chess.
powers of movement: n. The particular abilities that a piece has to move and capture. These powers come in the form of decision procedures or algorithms for determining from a given position which spaces a piece may legally move to. This comes in handy for allowing computers to play or referree Chess variants. Most pieces move and capture in the same way. For divergent pieces, the powers of movement will distinguish between how to separately identify capturing moves and non-capturing moves.
progressive chess: n. A type of game wherein white moves one piece, black moves two pieces, white moves three pieces, etc., increasing the number of pieces moved by one after each player's turn. See also: Progressive Chess Page
promotable: n. A starting piece that has an option to promote upon reaching a certain rank.
promote: n. To upgrade a piece's powers of movement or to replace it with a different piece. This is commonly done when the piece reaches a certain rank, though it may be done under other circumstances too.
promoted piece: n. A more powerful piece that is created by promoting a starting piece. (Compare starting piece.)
promotion zone: n. A predesignated portion of a chess board that a starting piece must reach in order to receive a promotion.
proprietary game: n. A chess variant that is developed and marketed for profit. Copyrights to the artwork and printed matter of a proprietary game are the property of the inventor and/or licensing company. Although the rules to a game may never be copyrighted (nor patented), the particular wording of the rules is usually copyrighted. Furthermore, any unique mechanism included with the game may be protected by a patent.
pseudo legal: adj. In compliance with most rules of the game, but not necessarily with those concerning exposure of a piece to capture.
This is mainly a programming term. Besides making code less complicated, it serves the function of avoiding the equivalent of the liar's paradox. Consider the statement, "This statement is false." If it's true, it's false, and if it's false, it's true. You could seesaw back and forth on whether it is true or false without any resolution. Now consider two long-ranging royal pieces, such as the royal Queen in Caïssa Britannia. This piece moves as a Queen but may not move through check. With just this information, let's now consider whether one can check the other. Suppose the Black Queen is on e7, nothing is on d6, and the White Queen moves to c5. This would be legal if the White Queen can check the Black Queen without being checked back. To check the Black Queen, it has to cross d6, and it can do this only if it would not be in check there. To know whether it would not be in check there, it will have to determine whether the Black Queen can move there. To determine whether the Black Queen can move there, it will have to know whether the White Queen can move there, and so on back and forth. This would result in infinite recursion and leave the question unanswered. To break out of this recursive loop, the concept of pseudo legality is employed. Pseudo legally, the two Queens would be checking each other in this position, because pseudo legality does not take into consideration whether they have to cross check to complete their moves. In fact, the rules of this game are consistent with this notion. The Queen's attack on another Queen is undeterred by the restriction that it cannot move through check.

Q

R

radial: In a direction that passes through the same number of dimensions in equal measure.
On a board with spaces at right angles, the radial directions are the orthogonal and diagonal directions. On a 3D board, they also include the 3D diagonal direction.; In a direction that goes from one adjacent space to the next.
This is a more general definition that works for hexagonal boards but loses the mathematical precision of the first definition.
rank: n. A complete horizontal row of spaces on a board. The second part of a coordinate normally designates the rank. (Compare file.)
rearward: In a direction that goes toward the side of the board a player's pieces began on.
relative value: n. The exchange value of a given piece with respect to other pieces.
reserve piece: n. An off-board piece that may be dropped onto the board to subsequently be used as one's own.
rider: n. A piece that serially repeats a single type of leap in the same outward direction. Having no natural limit, such a piece is an infinite mover. Although a leap cannot be blocked, a rider may be blocked when its series of leaps takes it to an occupied space. Examples from Chess include the Bishop, Rook, and Queen. (Dickins)
rifle piece: n. A piece that captures by shooting rather than by displacement, overtaking or some other means. [e.g.: The pieces of rifle chess.]
rifle capture: (See shot.)
right-angled spaces: Spaces whose shapes are made up of 90 degree angles, such as squares, rectangles, diamonds, intersections of perpendicular lines, and cubes. These spaces have the property that their number of axes matches the number of dimensions in the game. This allows for some mathematical equivalences between the coordinate system and the game's dimensions. Notably, hexagonal spaces are not right-angled, and some concepts have to be reinterpreted when using them.
river: n. On the Xiangqi board, a central horizontal division between the two sides of the board, beyond which Elephants cannot move and Pawns gain new powers of movement.
rotating piece: n. A heraldic piece that may rotate at the close of a move (or as a move in itself) in order to realign its powers of movement by an angle of 45°. (e.g.: A Bishop rotated 45° moves as a Rook.)
row: n. A one-dimensional cross-section of a board composed of right-angled spaces; a complete series of spaces connected along a single dimension. (Compare coordinal_plane); n. A complete series of spaces connected in a straight line through shared sides or shared faces.; n. Colloquially, a rank.
round chess: n. Chess played on a round board whereon the "squares" are delineated by radial lines and concentric circles.
royal piece: adj. Denotes a type of piece whose checkmate, capture, elimination, or sometimes other fate, terminates the game with a determination of its outcome.
The best known royal piece is the King. Chess and many other variants are won by checkmating the King, which involves creating a position in which it cannot escape capture. It is very likely that checkmate evolved from the goal of capture. This may be why Davidson has claimed in his *Short History of Chess* that the object of Chaturanga, the Indian precursor of Chess, was to capture the King. There are also more recent variants, such as Smess, where capturing the opponent's royal piece is what wins the game. In games where each player has more than one royal piece, the object may become elimination of all royal pieces, as in Tai Shogi. In the occassional variant, the object can become a different kind of fate for a royal piece. In Anti-King Chess, for example, the game is lost if a player's Anti-King becomes completely unchecked without a move to put it back in check.

S

screen

n. A single intervening piece that a hopper must leap over in order to move/capture.

sequence

n. In Progressive Chess, the series of moves that each player makes in a turn: White makes 1 move, black makes 2 moves, white makes 3 moves, and so on.

set

n. All of the pieces required to play a given game.

setup

n. (See initial setup.)

shogi

1. n. The most popular of Japanese chess variants, played on a 9x9 board and allowing drops. (See Shogi.)

2. n. Any chess game that allows drops.

3. n. The Japanese word for chess.

shoot

v. To capture without changing position.

shot

1. n. A capture that is made without changing position.

2. v. The past tense of the verb shoot.

side

n. One of the two or more armies competing in a chess game.

space

n. A discrete, designated location on a chess board that a piece may move to or from.

A space is sometimes called a square, because it frequently comes in that shape. But spaces do come in other shapes. On a hexagonal board, a space will be shaped as a hexagon. On a 3D board, it will be shaped as a cube. On a circular board, it will be shaped as a division of a pie wedge. And there are other types of boards with spaces in other shapes.

spherical chess

n. Chess played on a spherical board whereon the spaces are designated by longitude and latitude lines.

stalemate

n. A position characterized by a player's royal piece not being threatened, while at the same time, the player is unable to make a legal move.

standard move

n. A move to a space that is empty or occupied by an enemy piece that is captured by virtue of the move. (Compare passive move, capture move.)

standard piece

n. A piece having only standard move options. [e.g.: Knight, Bishop, Rook, Queen, King.]

starting piece

n. A piece that is a part of the initial array. (Compare promoted piece, reserve piece.)

starting space

1. n. A home square.

2. n. The space a piece begins its move from.

straight

adj. Another word for orthogonal

adv. Orthogonally

T

take: v. Another word for capture.
threatened: I>adj. Another word for attacked.
3-D board: n. An arrangement of 2-D boards used for playing 3-D chess. Typically, a number of 2-D boards are stacked vertically, with sufficient space between them to set up and manipulate the pieces. Some players, however, prefer the 2-D boards to be laid out on a flat surface--especially if the game is quite small.
3-D chess: three-dimensional chess) - n. A chess variant played on a 3-D board with pieces having additional powers that allow them to move three-dimensionally. (e.g., Raumschach.)
3-D diagonal: adj. In a direction that changes three dimensions at once in equal measure.
(1,1,1), (1,-1,-1), and (-1,1-1) are all examples of 3D diagonal movement. This should not be confused with the normal sense of diagonal, which still has a use on 3D boards.; adj. In a direction that passes through the opposite corners of a polyhedral 3D space, the most common shape being a cube.
For boards with cubic spaces, this definition is functionally equivalent to the preceding one and just provides a different way of visualizing the same concept.
trade: v. Another word for exchange.
transport: v. To move a piece to a position it could not reach by its own powers of movement. This may involve a special rule or the use of a piece that can transport another piece.
2-D board: n. An ordinary two-dimensional chess board, as opposed to a 3-D board. (e.g., the orthochess board.)

U

unit: n. Another word for a chess piece.
usual chess: n. Another name for Orthodox Chess.

V

values

n. (See relative values.)

variant

n. (See chess variant.)

vertical

adj. In a direction that goes only through the second dimension, which is forward and backward (or figuratively north and south) on a board composed of square spaces. (Compare horizontal.)

In normal algebraic notation, the second part of the coordinate is a number referring to the rank. A move that changes only the rank, such as a1 to a8, moves through the second dimension.

In normal English, vertical describes a direction going through the third dimension, as in up and down. This is why people get vertigo from heights, not from distance. The usage for the second dimension on the chess board might have come from viewing chess and chess variants on computer screens, on which the second dimension is portrayed vertically, or it might come from studying chess problems in an upright position. Because of this usage, I am suggesting altitudinal for the normal meaning of vertical.

W

Wazir: n. (Arabic for vizier) An elemental piece. Moves to an orthogonally adjacent square.
wraparound: n. A rule variation that allows pieces to exit the board on one side (or end) and re-enter the board on the opposite side (or end), in a continuous move, as though the board were rolled into a cylinder. (See cylindrical chess.)

X

X-Y leaper: n. Where X and Y are both integer values, a leaper that can leap X ranks and Y files or X files and Y ranks away. For pieces on a hexagonal board, use any pair of the three different orthogonal rows instead of just the two used to define coordinates. (See elemental piece.)
xiangqi: n. The worlds most popular chess variant, originating in China. (See xiangqi.)

adjacent square	distant square
air square	pass-through square
arrival square	departure square
attack	defend
board move	drop
capture leap	passive leap
capture move	passive move
capture square	passive square
compound piece	elemental piece
defend	attack
departure square	arrival square
diagonal direction	orthogonal direction
diagonally adjacent squares	orthogonally adjacent squares
distant square	adjacent square
drop	board move
drop piece	starting piece
elemental piece	compound piece
endgame	opening
enemy piece	friendly piece
file	rank
finite mover	infinite mover
forward diagonals	rearward diagonals
friendly piece	enemy piece
heterodox chess	orthodox chess
horizontal direction	vertical direction
infinite mover	finite mover
leap	line move
leaper	line piece
leap passively	leap to capture
leap to capture	leap passively
line move	leap
line piece	leaper
move obliquely	move radially
move passively	move to capture
move radially	move obliquely
move to capture	move passively
oblique move	radial move
oblique square	radial square
opening	endgame
orthodox chess	heterodox chess
orthogonal direction	diagonal direction
orthogonally adjacent squares	diagonally adjacent squares
passive leap	capture leap
passive move	capture move
passive square	capture square
pass-through squares	air squares
points	squares
promoted piece	starting piece
radial move	oblique move
radial square	oblique square
rank	file
rearward diagonals	forward diagonals
reserve piece	starting piece
squares	points
standard move	passive move or capture move
standard square	passive square or capture square
starting piece	reserve piece or promoted piece
straight-forward	straight-rearward
straight-rearward	straight-forward
vertical direction	horizontal direction