late 14c.; see checkmate (n.). Related: Checkmated; checkmating.

mid-14c., from Old French eschec mat (Modern French échec et mat), which (with Spanish jaque y mate, Italian scacco-matto) is from Arabic shah mat "the king died" (see check (n.1)), which ac [..]

(n) complete victory(n) a chess move constituting an inescapable and indefensible attack on the opponent's king(v) place an opponent's king under an attack from which it cannot escape and th [..]

in the game of chess, means placing your adversary’s king in such a position that he can neither cover nor move out of check. Figuratively, “to checkmate” means to foil or o [..]

According to the rules, and idly confirmed by the Chess Glossary Team, this is Game Over - if this has happened to your King, you've lost.

Threatening the capture of the enemy king such that it cannot escape. This wins the game for the attacking side.