n. A common gambling card game in casinos, where the object is to get as close to 21 without going over.n. A hand in the game of blackjack consisting of a face card and an ace.n. The flag (i.e., a jack) traditionally flown by pirate ships; popularly thought to be a white skull and crossed bones on a black field (the Jolly Roger). In older literature sometimes spelled "black jack".n. a small, flat, blunt, usually leather-covered instrument loaded with heavy material such as lead or ball bearings.n. a type of weed, Bidens pilosa, in the family Compositae.v. To strike with a blackjack or similar weapon.