Etymology
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jack (n.)
late 14c., jakke "a mechanical device," from the masc. name Jack. The proper name was used in Middle English for "any common fellow," and thereafter extended to various appliances which do the work of common servants (1570s). Also used generically of male animals (1620s, see jackass, jackdaw, etc.).

As a portable contrivance for raising weight by force from below, 1703. As the name of a device for pulling off boots from 1670s. The jack in a pack of playing cards (1670s) is in German Bauer "peasant." Slang meaning "money" is by 1890 (in earlier slang it meant "a small coin"). Jack-towel, one sewn together at the ends round a roller, is from 1795. The jack of Union Jack is a nautical term for "small flag at the bow of a ship" (1630s) and perhaps is from the word's secondary sense of "smaller than normal size."
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jack (v.)
1860, jack up "hoist, raise, lift with a jack," American English, from jack (n.) in the appliance sense. Figurative sense "increase (prices, etc.)" is 1904, American English. Related: Jacked; jacking. Jack off (v.) "masturbate" is attested from 1916, probably from jack (n.) in the old slang sense of "(erect) penis."
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jack-shit (n.)
"nothing at all," 1968, U.S. slang, from jack (n.) + shit (n.).
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jack-hammer (n.)
also jackhammer, "portable rock-drill worked by compressed air," 1913, from jack (n.) + hammer (n.). As a verb by 1947. Related: Jack-hammered; jack-hammering.
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jack-knife (n.)
also jackknife, "pocket knife larger than a pen-knife," 1711, probably American English, apparently from some sense of jack (n.). Perhaps it originally was associated with sailors. Jackleg, jacklegged was a U.S. colloquial term of contempt from 1839. Scottish dialect had jockteleg (1670s) "large clasp-knife," of unknown origin, also jackylegs, jack-o-legs. As a kind of swimming dive from 1922; as a type of tractor-trailer accident, 1966; both from the notion of folding, as the knife does.
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jack-in-the-box (n.)
also jack-in-a-box, 1560s, a name for a sharp or cheat, "who deceived tradesmen by substituting empty boxes for others full of money" [Robert Nares, "A Glossary of Words, Phrases, Names, and Allusions," London, 1905]. See Jack + box (n.1). As a type of toy involving a figure on a spring inside a box, it is attested by 1702. Also it has been used variously to mean "peddler who sells wares from a temporary stall" (1690s), "an unborn child," a type of gambling game, a hermit crab, a large wooden male screw, the sacrament, and various mechanical devices.
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jakes (n.)
"a privy," mid-15c., genitive singular of jack (n.), perhaps a humorous euphemism.
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jackaroo (n.)
Australian for "a new arrival from Britain," 1867, from Jack + ending from kangaroo. The female counterpart jillaroo is attested from 1945.
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applejack (n.)
also apple-jack, "apple-brandy, liquor distilled from cider," 1816, from apple + jack (n.).
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steeplejack (n.)
"one who climbs steeples, chimneys, etc. to make repairs," 1881, from steeple + jack (n.) "fellow, man."
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