A blackjack is a short, thick stick that is used as a weapon. [US, informal] Police confiscated guns, knives and blackjacks. regional note: in BRIT, use truncheon.

Cards. Also called twenty-one [twen-tee-wuhn, twuhn-] /tw[n tiwn, twn ti-/ . a gambling game in which the object is to obtain from the dealer cards whose values add up to, or close to, 21 but do not exceed it.