a chess move constituting an inescapable and indefensible attack on the opponent's king
source: WordNet 3.0
The position in the game of chess when a king is in check and cannot be released, -- which ends the game.
source: Webster 1913
verb
place an opponent's king under an attack from which it cannot escape and thus ending the game
Kasparov checkmated his opponent after only a few moves.
source: WordNet 3.0
To check (an adversary's king) in such a manner that escape in impossible; to defeat (an adversary) by putting his king in check from which there is no escape.
