twenty-one

US: (twen′tē wun′, twun′-)

WordReference Random House Learner's Dictionary of American English © 2025

ˈtwen•ty-ˈone,  n. 

1. Games blackjack (def. 2a).

WordReference Random House Unabridged Dictionary of American English © 2025

twen•ty-one  (twen′tē wun′, twun′-), 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. Games 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.

adj. 

5. amounting to 21 in number.

Collins Concise English Dictionary © HarperCollins Publishers::

twenty-one noun

1. another name (esp US) for pontoon21