Blackjack meaning : A common gambling card game in casinos, where the object is to get as close to 21 without going over. A hand in the game of blackjack consisting of a face card and an ace. 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). 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. Any of several species of weed of genus Bidens, such as Bidens pilosa, in the family Compositae. A blackjack oak. To strike with a blackjack or similar weapon.