- A lever for depressing the sinkers which push the loops down on the needles in a knitting machine.
- (nautical) A naval ensign flag flown from the main mast, mizzen mast, or the aft-most major mast of (especially) British sailing warships; Union Jack.
- A jackfruit tree.
- A compact, portable machine for planing metal.
- (slang) Money.
- A hood or other device placed over a chimney or vent pipe, to prevent a back draught.
- A large California rockfish.
- A male animal.
- (nautical) A bar of iron athwart ships at a topgallant masthead, to support a royal mast, and give spread to the royal shrouds; also called jack crosstree.
- (obsolete) A pitcher or can of waxed leather, supposed to resemble a jackboot; a black-jack.
- (archaic) A knave (a servant or later, a deceitful man).
- A device to pull off boots.
- (sports) A target ball in bowls, etc; a jack-ball.
- (mining) A wooden wedge for separating rocks rent by blasting.
- (nautical) A small flag at the bow of a ship.
- A coarse mediaeval coat of defence, especially one made of leather.
- A machine for twisting the sliver as it leaves the carding machine.
- A penny with a head on both sides, used for cheating.
- A system of gearing driven by a horse power, for multiplying speed.
- A common name for the freshwater pike, green pike or pickerel.
- A man or men in general.
"Every man jack."
- (obsolete, nautical) A sailor, a jacktar.
- (card games) The card ranking between the ten and queen of any suit, picturing a knave or prince on its face. In some card games has a value of eleven based on its rank, but in many card games has a value of ten like the ten, queen, and king cards. Also called a knave.
- In hunting, the pan or frame holding the fuel of the torch used to attract game at night; also, the light itself.
- Electrical connector in a fixed position (see Gender of connectors and fasteners)
- A mechanical contrivance, an auxiliary machine, or a subordinate part of a machine.
- A surface-mounted connector for electrical, especially telecommunications, equipment.
- A machine for turning a spit; a smokejack.
- (colloquial, euphemistic) Nothing,
"You haven't done jack. Get up and get this room cleaned up right now!"
- A grating to separate and guide the threads in a warping machine; a heck box.
- (military) A coarse and cheap medieval coat of defense, especially one made of leather.
- A machine for slicking or pebbling leather.
- (slang, Appalachians) A smooth often ovoid large gravel or small cobble in a natural water course.
- A mechanical device used to raise and (temporarily) support a heavy object, e.g. screw jack, scissor jack, hydraulic jack, ratchet jack, scaffold jack.
"She used a jack to lift her car and changed the tire."
- In the harpsichord, an intermediate piece communicating the action of the key to the quill; also called hopper.
- Any marine fish or the species of the Carangidae family.
- A donkey.
- Female ended electrical connector (see Electrical connector)
- (Britain, dialect, obsolete) A drinking measure holding half a pint or, sometimes, a quarter of a pint.
- Mangifera caesia, related to the mango tree.
- A sawhorse or sawbuck.
- (games) A small, six-pointed playing piece used in the game of jacks.
- (intransitive) To dance by moving the torso forward and backward in a rippling motion.
- (transitive) To use a jack.
"He jacked the car up so that he could replace the brake pads."
- (transitive, colloquial) To steal something, typically an automobile. Shortened form of carjacking.
"Someone jacked my car last night!"
- To produce by freeze distillation; to distil (an alcoholic beverage) by freezing it and removing the ice (which is water), leaving the alcohol (which remains liquid).
- (transitive, slang, baseball) To hit (the ball) hard; especially, to hit (the ball) out of the field, producing a home run.
- (transitive) To raise or increase.
"If you want to jack your stats you just write off failures as invalid results."