Pronunciation: (twen'tē-wun', twun'-),[key] —n. 1. a cardinal number, 20 plus 1.
2. a symbol for this number, as 21 or XXI.
3. a set of this many persons or things.
4. Also,21.Also called blackjack. a gambling game at cards, in which the object is to obtain from the dealer cards whose values add up to, or close to, 21 but which do not exceed it.