Etymology
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Jack 

masc. proper name, attested by 1218, probably via Anglo-French Jake, Jaikes, from Old French Jacques (which was a diminutive of Latin Jacobus; see Jacob), but in English the name always has been regarded as a familiar form of John, and some have argued that it is a native formation. In Middle English spelled Jakke, Jacke, etc., and pronounced as two syllables ("Jackie").

In England, Jack became a generic name applied familiarly or contemptuously to anybody (especially a young man of the lower classes) from late 14c. Later used especially of sailors (1650s; Jack-tar is from 1781); Jack-ashore (adj.) "drinking and in high spirits, recklessly spending" (1875) also is an image from sailors (1840 as a book title). In U.S., as a generic name addressed to an unknown stranger, attested from 1889. Every man Jack "everyone" is from 1812. Also see jack (n.).

Used in male personifications from 15c.; first record of jack-of-all-trades "person handy at any kind of work or business" is from 1610s; Jack Frost is from 1826; Jack-nasty "a sneak or sloven" is from 1833 (Jack-nasty-face, a sea-term for a common sailor, is from 1788). Jack Sprat for a small, light man is from 1560s (his opposite was Jack Weight). Jack-pudding "comical clown, buffoon" is from 1640s. Jack-Spaniard is from 1703 as a Spaniard, 1833 as "a hornet" in the West Indies. Other personifications listed in Farmer & Henley include jack-snip "a botching tailor," Jack-in-office "overbearing petty official" (1680s), Jack-on-both-sides "a neutral," Jack-out-of-doors "a vagrant" (1630s), jack-sauce "impudent fellow" (1590s).

The U.S. plant jack-in-the-pulpit (Indian turnip) is attested by 1833. Jack the Ripper was active in London 1888. The Scottish form is Jock (compare jockey (n.)). Alliterative coupling of Jack and Jill is from 15c. (Iakke and Gylle, Ienken and Iulyan). Jack Ketch for "hangman, executioner" (1670s) is said to be from the name of a public executioner in the time of James II (compare Derrick); it also was used as a verb meaning "to hang."

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Union Jack 
1670s, from union + jack (n.); properly a small British union flag flown as the jack of a ship, but it has long been in use as a general name for the union flag. The Union flag (1630s) was introduced to symbolize the union of the crowns of England and Scotland (in 1603) and was formed of a combination of the cross saltire of St. Andrew and the cross of St. George. The cross saltire of St. Patrick was added 1801 upon the union of parliaments of Great Britain and Ireland.
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Jack-o'-lantern (n.)
also jack-o-lantern, jack-a-lantern, jackolantern, 1660s, "night-watchman;" 1670s as a local name for a will-o-the-wisp (Latin ignis fatuus), mainly attested in East Anglia but also in southwestern England. Literally "Jack of (with) the lantern;" see Jack + lantern. The extension to carved pumpkin lanterns is attested by 1834 in American English.
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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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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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Jill 
fem. proper name, Middle English Jille, Jylle, Gille, etc., familiar shortening of Jillian, Gillian, which represent the common Middle English pronunciation of Juliana (see Gillian). A very popular name for girls in medieval England, hence its use as a familiar, almost generic, name for a girl (early 15c.; paired with Jack since mid-15c.).
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Jenny 

fem. personal name, originally another form of Jane, Janey and a diminutive of Jane or Janet; in modern use (mid-20c.) typically a shortening of Jennifer. Jenny is attested from c. 1600 as female equivalent of jack (n.), and like it applied to animals (especially of birds, of a heron, a jay, but especially Jenny wren, 1640s, in bird-fables the consort of Robin Redbreast). Also like jack used of machinery; Akrwright's spinning jenny (1783) is said to have been named for his wife, but is perhaps rather a corruption of gin (n.2) "engine."

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Jacksonian 
1824, of or in the character of U.S. politician Andrew Jackson (1767-1845). The surname is recorded from early 14c., literally "Jack's son, son of a man named Jack." Jacksonville, Florida, was renamed for him in 1822 from earlier Cowford, said to be an English translation of a native name wacca pilatka [Room].
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Tib 

1530s, typical name for an English woman of the lower class, hence "girl, lass, sweetheart," sometimes also "strumpet," from the pet form of Isabel. Often paired with Tom, as Jill was with Jack. Colloquial St. Tibb's Eve (1785) was the evening of the last day, the Day of Judgment, hence "never."

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