Real Dictionary

checkmate
uncountable noun: In chess, checkmate is a situation in which you cannot stop your king being captured and so you lose the game.

checkmate in American English
the move that wins the game by checking the opponent's king so that it cannot be protected
to place in checkmate
used to signify that one's opponent's king is in checkmate
interjection: (used by a player to announce that he or she has put the opponent's king into inextricable check.)
noun: an act or instance of maneuvering the opponent's king into a check from which it cannot escape, thus bringing the game to a victorious conclusion
transitive verb: to maneuver (an opponent's king) into a check from which it cannot escape; mate

checkmate in British English
to place (an opponent's king) in checkmate
exclamation: a call made when placing an opponent's king in checkmate
noun: the winning position in which an opponent's king is under attack and unable to escape