1 [count] : a device used for lifting something heavy (such as a car) 2 [count] : a playing card that has a picture of a soldier or servant and that is worth more than a ten and less than a queen
▪ the jack of hearts/spades/clubs/diamonds — see picture at playing card 3 [count] : a small opening where something connects with a wire to something else
▪ a telephone/stereo jack 4 a [count] : a small usually metal object that has six points and that is used in the game of jacks
b jacks [plural] : a child's game in which jacks are thrown and picked up while bouncing and catching a small ball
▪ children playing jacks 5 [noncount] US slang : anything at all — used in negative statements ▪ You don't know jack. = (offensive) You don't know jack shit.