1 [U,C] (in tennis) the situation when both players have 40 as a score, after which one player must win two points one after the other in order to win the game
2 [C] (AmE) a playing card with two PIPS on it:
the deuce of clubs
3 (the deuce) [sing.] (old-fashioned, spoken) used in questions to show that you are annoyed:
What the deuce is he doing?
