Etymology
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skipjack (n.)
1550s, "a pert shallow-brained fellow; a puppy, a whipper-snapper; a conceited fop or dandy" [OED], from skip (v.) + generic name jack (n.). Applied 1703 to tropical fishes with leaping tendencies. In reference to a kind of sailing boat used on Chesapeake Bay, attested from 1887.
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Jock 
c. 1500, variant of the masc. proper name Jack, the by-form of John. In Scotland and northern England it is the usual form. Since 1520s, like Jack, it has been used generically, as a common appellative of lads and servants, as the name of a typical man of the common folk, of a Scottish or North Country seaman, etc.
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blackjack (n.)
used in various senses since 16c., earliest is possibly "tar-coated leather jug for beer" (1590s), from black (adj.) + jack in any of its many slang meanings. From 1867 as "pirate flag." The hand-weapon so called from 1889; the card game by 1900.
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jack-rabbit (n.)
also jackrabbit, large prairie hare, 1863, American English, shortening of jackass-rabbit (1851; see jackass + rabbit (n.)); so called for its long ears. Proverbial for bursts of speed (up to 45 mph).
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billy (n.)
"club," 1848, American English, originally burglars' slang for "crowbar;" meaning "policeman's club" first recorded 1856, probably from nickname of William, applied to various objects (compare jack, jimmy, jenny). But compare French bille "a short, stout stick" (see billet (n.1)). Billy-goat as a familiar name for a male goat is from 1826.
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zany (n.)
comic performer, 1580s, from French zani, from Italian zani, zanni "a zany, clown," originally Zanni, Venetian dialect variant of Gianni, pet form of Giovanni "John;" thus equivalent to English Jack. A stock character in old comedies, he aped the principal actors.
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natterjack (n.)

common toad of western and north-central Europe (rare in Britain) with a yellow stripe on its back, a distinctive running gait, and a loud mating call, 1769; the second element probably is the proper name jack (q.v.); for first element, Weekley suggests connection with attor "poison" (see attercop); it also could be echoic of its croaking.

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jackdaw (n.)

1540s, "the common daw," a type of small European crow (Corvus monedula), "which frequents church towers, old buildings, etc.; noted for its loquacity and thievish propensities" [OED]. See jack (n.) + daw.

In modern times, parrots are almost the only birds that have the gift of speech, though connoisseurs are not ignorant that starlings and jackdaws have good abilities in that way, when properly educated. ["Chambers' Home Book and Pocket Miscellany," 1853]

In U.S. sometimes applied to a species of grackle.

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Jacquerie (n.)

"French peasantry," 1520s, from French jacquerie "peasants or villeins collectively" (15c.), from Jacques, the proper name, which is used as Jack is used in English, in the sense of "any common fellow." So it also means "the rising of the northern French peasants against the nobles in 1357-8," from a French usage. Etymologically, Jacques is from Late Latin Iacobus (see Jacob).

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Jack Russell 
type of terrier (not recognized as a distinct breed), 1907, named for the Rev. John Russell (1795-1883) of Devonshire, "the sporting parson."
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