blackjack

1 [black + jack (vessel)] :  a tankard for beer or ale usually of tar-coated leather

2 :  sphalerite

3 :  a hand weapon typically consisting of a piece of leather-enclosed metal with a strap or springy shaft for a handle

4 :  an often scrubby oak (Quercus marilandica) chiefly of the southeastern U.S. —called also blackjack oak

5a :  a card game the object of which is to be dealt cards having a higher count than those of the dealer up to but not exceeding 21 —called also twenty-one, vingt-et-unb :  an ace and a face card or ten as the first two cards dealt to a player in the game of blackjack —called also natural, twenty-one