Definition of blackjacks:
(n) :
(card games) A common gambling card game in casinos, where the object is to get as close to 21 without going over.
(n) :
(card games) A hand in the game of blackjack consisting of a face card and an ace.
(n) :
(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).
(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).
(n) :
(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.
(n) :
(aviation) A tool of leather filled with shot (or similar), resembling the weapon, used for shaping sheet metal.