1. (noun)blackjack oak, blackjack, jack oak, Quercus marilandica a common scrubby deciduous tree of central and southeastern United States having darkbark and broad three-lobed (club-shaped) leaves; tends to form dense thickets
4. (verb)blackjack, twenty-one, vingt-et-un a gambling game using cards; the object is to holdcards having a higher count than those dealt to the banker up to but not exceeding 21
5. (verb)blackmail, blackjack, pressure exert pressure on someone through threats