Definition of jack:
- A diminutive of John; a saucy or paltry fellow; a sailor; any instrument that supplies the place of a boy, as a boot- jack; a portable machine for raising great weights through a small space; a contrivance to turn a spit; a young pike; a coat of mail; a pitcher of waxed leather; a small bowl thrown out for a mark to the bowlers; the male of certain animals; a horse or wooden frame on which wood or timber is sawed; the knave of cards; a flag, ensign, or colour, displayed from a staff on the end of a bowsprit. Jack of all trades, a person who can turn his hand to any kind of business. Jack by the hedge, a piant growing under hedges. Jack in a box, a plant; a large wooden male screw, turning in a female one; a figure made to start out of a box. Jack in office, one who assumes authority on account of his office. Jack of the clock- house, a little man that strikes the quarters in a clock. Jack with a lantern, an ignis fatuns, or will- o- the- wisp. Union Jack. See Union.
- A name applied as an expression of familiarity; any mechanical contrivance for replacing the personal service of an attendant; a screw for raising heavy weights; a contrivance to turn a spit; any timber cut short of its usual length; a flag or ensign; a sailor - usually in composition, as jack- tar; a prefix signifying male, as jack- ass.
- A homely substitute for a coat of mail; a short loose coat terminating at the waist.