(fandom slang) A fan of the South Korean girl group 2NE1.

(card games) A common gambling card game in casinos, where the object is to get as close to 21 without going over.

(card games) A hand in the game of blackjack consisting of a face card and an ace.

(card games) A variant of switch where each player is initially dealt the same number of cards, usually seven, and when one player plays a black jack the player whose turn comes next has to pick up that many cards, unless they play a red jack (as this normally cancels a black jack).

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).

(weaponry) A small, flat, blunt, usually leather-covered weapon loaded with heavy material such as lead or ball bearings, intended to inflict a blow to the head that renders the victim unconscious with diminished risk of lasting cranial trauma.

(aviation) A tool of leather filled with shot (or similar), resembling the weapon, used for shaping sheet metal.

Any of several species of weed of genus Bidens, such as Bidens pilosa, in the family Compositae.

Ellipsis of blackjack oak.

Any of a series of hard, dark soils, often considered low quality, but suitable for growing certain crops such as cotton.

(pharmacology, UK, Australia, rare) Ammonium bituminosulfonate.

To strike with a blackjack or similar weapon.