Green’s Dictionary of Slang

1. (US) a donkey or jackass.

1785		G. Washington Diaries II 458: Dispatched at his own reqt. the Spaniard who had the charge of my Jack from Spain .
1829		T. Hood ‘Epping Hunt’ Works (1862) II 310: Some long-eared jacks, some knacker’s hacks.
1843		R.S. Surtees Handley Cross (1854) 79: Three donkeys, two jacks and a jinney.
1864		Ohio State Board of Agriculture Annual Report XVIII 3: The class of Jacks and Mules be changed.
1892		L.A. Times 9 Dec. 11/3: Water [...] is [...] packed in on jacks — desert canaries — (of which we are blest in superabundance).
1908		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:iv 323: jack, n. [...] 3. A jackass.
1944		Democrat 2 Nov. 3/4: For Sale — One Tennessee jack, 12 to 14 years old, weight about 700 pounds, $250 [DA].
1948		in Randolph & Legman Ozark Folksongs and Folklore (1992) II 712: He hazed both his jacks towards Kill-Pecker Creek.
1970		G. Scott-Heron Vulture (1996) ix: There’s a story I heard once about a jackass that was set down squarely between two bales of hay and starved to death. I was just like Jack.
a.1986		‘Old Zebra Dun’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 82: Then he said, ‘My jack is weary, there are sev’ral hills to cross. / I want to trade my burro for a gentle riding hawse.’.

2. (US) a flapjack.

1832		J.P. Kennedy Swallow Barn I 57: She was usually occupied in paring apples to be baked up into tough jacks for our provender [DA].
1850		W. Ryan Personal Adventures in [...] Calif. I 238: Frederic, Halliday, and myself, set to work upon the ‘jacks,’ and soon tossed up a sufficiency for our purpose.

3. a blackjack or cosh.

1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor IV 348/2: He had first to remove an iron bar at the first floor landing window to the back, which he did with his jack.
1893		J. Hawthorne Confessions of Convict 92: The screw and the jack, the most powerful tools in a burglar’s kit.
1911		G. Bronson-Howard Enemy to Society 154: One of them’ll push you, you’ll push him back, an argument’ll start and the first thing you know yuh’re laid out with a jack.
1918		T.A. Dorgan in Zwilling TAD Lex. (1993) 111: I had to bounce jack over the guy’s noodle before he’d loosen up.
1931		D. Runyon ‘Earthquake’ in Runyon on Broadway (1954) 161: He is known to boff guys on their noggins with this jack.
1943		R. Llewellyn None But the Lonely Heart 331: Specially them little jobs with the jack.
1950		Goldin et al. DAUL 109/1: Jack, n. 1. A blackjack.
1967		in S. Harris Hellhole 151: And he hit her on the behind with his jack.
1973		E. Droge Patrolman 25: Just about the only time you’ll see an officer with a billy instead of a jack (a lead club, covered with leather) in his back pocket is when he is [...] attached to the academy.

4. a jackal.

1984

Partridge DSUE (8th edn) 606: from ca. 1890.

5. (US/Can.) a lumberjack.

c.1900		F. Rickaby Ballads and Songs of the Shanty-Boy (1926) 97: Every jack’s a cant-hook man; no others can be found. They do some heavy loggin’, but they do it best in town [DA].
1931		J. Stevens ‘Fisherman’s Paradise’ in Botkin Folk-Say 125: Paul Bunyan’s ’jacks were exhausted by the hardest log drive of timber-county history.
1947		Sat. Eve. Post 8 Mar. 20/1: The red-bearded jack came on again, head low and shielded [DA].

6. (US) a jackpot.

1905

H. Green Actors’ Boarding House (1906) 105: Smith’s friend won the first jack.

7. a jacket.

1962

F. Norman Guntz 88: Like all that leather jack jazz.