Online Etymology Dictionary

J: the letter is a late modification of Roman -i-, originally a scribal creation in continental M.L. to distinguish small -i- in cursive writing from the strokes of other letters, especially in the final positions of words. But in Eng., -y- was used for this, and -j- was introduced c.1600-1640 to take up the consonantal sound that had evolved from -i- since L.L. times. This usage first was attested in Sp., where it was in place before 1600. Eng. dictionaries continued to lump together words beginning in -i- and -j- until 19c.
j'accuse: Fr., lit. "I accuse," phrase made famous by Emile Zola in a public letter attacking the irregularities of the Dreyfus trial (published Jan. 13, 1898).
jab: 1825, "to thrust with a point," Scot. variant of job "to strike, pierce, thrust," from M.E. jobben "to jab, thrust, peck" (c.1490), of unknown origin, perhaps echoic. Noun meaning "a punch with the fist" is from 1889. Sense of "injection with a hypodermic needle" is from 1914.
jabber (v.): c.1440, jablen, javeren, jaberen, probably echoic.
Jabberwocky: 1872, nonsense word (perhaps based on jabber) coined by Lewis Carroll, for the poem of the same name, which he published in "Through the Looking-Glass." The poem is about a fabulous beast called the Jabberwock.
jacinth: c.1230, an ancient blue gem (probably sapphire), from O.Fr. iacinte, from L. hyacinthus (see hyacinth). In modern use, a reddish-orange gem.
Jack: masc. proper name, 1218, probably an Anglicization of O.Fr. Jacques (which was a dim. of L. Jacobus, see Jacob), but in Eng. the name always has been associated with Johan, Jan "John," and some have argued that it is a native formation. Alliterative coupling of Jack and Jill is from 15c. (Ienken and Iulyan). As a generic name addressed to an unknown stranger, it is attested from 1889 in Amer.Eng. Used especially of sailors (1659; Jack-tar is from 1781).
jack (n.): late 14c., jakke "a mechanical device," from the name Jack. Used by 14c. for "any common fellow" (mid-14c.), and thereafter extended to various appliances replacing servants (1570s). Used generically of men (jack-of-all-trades, 1610s), male animals (1620s, see jackass, jackdaw, etc.), and male personifications (1520s, e.g. Jack Frost). The jack in a pack of playing cards (1670s) is in Ger. Bauer "peasant." Jackhammer is from 1930. Jack shit "nothing at all" is 1970s southern U.S. student slang. The jack of Union Jack is a nautical term for a small flag at the bow of a ship (1630s).
jack (v.): 1873, jack up, originally "abandon, give up," later (1885) "hoist with a jack;" then "increase prices, etc." (1904, Amer.Eng.), all from the noun. Jack off (v.) "to masturbate" is attested from 1916, probably from jack in the sense of "penis."
Jack o'lantern: 1663, a local name for a Will-o-the-wisp (L. ignis fatuus), mainly attested in East Anglia but also in southwestern England. The extension to carved pumpkins is 1837, Amer.Eng.
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."
jack-in-the-box: 1570, originally 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]. As a type of toy, it is attested from 1702.
jack-knife: 1711, perhaps so called because it originally was associated with sailors. As a type of dive, from 1922. The verb is attested from 1776.
jackal: c.1600, from Turk. çakal, from Pers. shaghal, from Skt. srgala-s, lit. "the howler." Figurative sense of "skulking henchman" is from the old belief that jackals stirred up game for lions.
jackanapes: c.1449, "a monkey," also "an impertinent, conceited fellow;" apparently from Jack of Naples, but whether this is some specific personification or folk etymology of jack (n.) + ape is unknown.
jackass: 1727, from jack (n.) + ass (q.v.). Meaning "stupid person" is attested from 1823.
jackboot: 1686, type of large, strong cavalry boot of 17c.-18c., later a type worn by Ger. soldiers in the Nazi period. From jack (q.v.), though the exact sense here is unclear + boot. Figurative of military oppression since 1768.
jackdaw: 1543, the common name of the daw (Corvus monedula), "which frequents church towers, old buildings, etc.; noted for its loquacity and thievish propensities" [OED]. See jack (n.) + daw.
jacket: mid-15c., from M.Fr. jaquet, dim. of O.Fr. jaque, a kind of tunic, probably from Jacque, the male proper name, also the generic name of a French peasant (see jacquerie), but possibly associated with jaque (de mailles) "short, tight-fitting coat," originally "coat of mail," from Sp. jaco, from Arabic shakk "breastplate." Iakke "a short, close-fitting upper garment" is attested in English from late 14c. Meaning "paper wrapper of a book" is first attested 1894.
jackpot: "big prize," 1944, from obsolete poker sense (1881) of progressive antes that begin when no player has a pair of jacks or better. Earlier, in criminal slang, it meant "trouble," especially "an arrest" (1902).
jackrabbit: 1863, Amer.Eng., shortening of jackass-rabbit, so called for its long ears.
Jacksonian: 1824, of or in the character of U.S. politician Andrew Jackson (1767-1845).
Jacob: masc. proper name, name of O.T. patriarch, son of Isaac and Rebecca and father of the founders of the twelve tribes, from L.L. Jacobus, from Gk. Iakobos, from Heb. Ya'aqobh, lit. "one that takes by the heel" (Gen. xxviii.12), a derivative of 'aqebh "heel." Most popular name form boys born in the U.S. from 1999 through 2008.
Jacobean: 1770, lit. "of James" (king or apostle), especially "of the literary and architectural style of the time of James I" (1844). See James.
Jacobin: early 14c., of the order of Dominican friars whose order built its first convent near the church of Saint-Jacques in Paris. The Revolutionary extremists took up quarters there 1789. Used generically of radicals and reformers since 1793.
jacquerie: 1523, from M.Fr., from O.Fr. jaquerie "peasants or villeins collectively," from Jacques, the proper name, which is used as Jack is used in Eng., in the sense of "any common fellow." So, also, "the rising of the northern Fr. peasants against the nobles, 1357-8."
Jacuzzi: 1966, U.S. proprietary name, from Jacuzzi Bros., Inc., Little Rock, Arkansas.
jade (1): "gemstone," 1590s, from Fr. le jade, error for earlier l'ejade, from Sp. piedra de (la) ijada (1569), "stone of colic, pain in the side" (jade was thought to cure this), from V.L. *iliata, from L. ilia (pl.) "flanks, kidney area."
jade (2): "worn-out horse," late 14c., possibly from O.N. jalda "mare," from Finno-Ugric (cf. Mordvin al'd'a "mare"). As a term of abuse for a woman, it dates from 1560.
jaded: "bored by continual indulgence," 1630s; pp. adj. from jade (2).
jag (n.): "period of unrestrained activity," 1887, Amer.Eng. from sense "load of hay or wood" (1597), of unknown origin, used in U.S. colloquial speech from 1834 to mean "a quantity, a lot."
jagged: 1440, from obs. verb jaggen (1373) "to notch or nick," Scot. and northern English, of unknown origin. Originally of garments with regular "toothed" edges; meaning "with the edge irregularly cut" is from 1577.
jaguar: big cat of the Americas (Felis onca), 1604, from Port. jaguar, from Tupi jaguara, said to be a name "denoting any larger beast of prey." Also a type of British-made car; in this sense the abbreviation Jag is attested from 1959.
Jah: 1539, a form of Heb. Yah, short for Yahweh "Jehovah." Used in some Eng. bibles. Cognate with the second element in hallelujah and Elijah.
jai alai: 1910, from Basque, from jai "celebration" + alai "merry."
jail: c.1275, gayhol, from O.N.Fr. gaiole and O.Fr. jaole, both meaning "a cage, prison," from M.L. gabiola, from L.L. caveola, dim. of L. cavea "cage." Both forms carried into M.E.; now pronounced "jail" however it is spelled. Norman-derived gaol (preferred in Britain) is "chiefly due to statutory and official tradition" [OED]. The verb "to put in jail" is from 1604. Jailbird is 1603, an allusion to a caged bird. Jail-break "prison escape" is from 1910. Jail bait "girl under the legal age of consent" is attested from 1934.
Jain: 1805, from Hindi Jaina, from Skt. jinah "saint," lit. "overcomer," from base ji "to conquer," related to jayah "victory." The sect dates from 6c. B.C.E.
jalapeño: from Mex.Sp. Jalapa, place in Mexico, from Aztec Xalapan, lit. "sand by the water," from xalli "sand" + atl "water" + -pan "place."
jalopy: "battered old automobile," 1924 (early variants include jaloupy, jaloppi, gillopy), of unknown origin; perhaps from Jalapa, Mexico, where many U.S. used cars were sent (see jalapeño).
jalousie: 1766, from Fr., lit. "jealousy" (see jealous), from notion of looking through blinds without being seen.
jam (v.): "to press tightly," also "to become wedged," 1706, of unknown origin, perhaps a variant of champ (v.). Sense of "to cause interference in radio signals" is from 1914. Jazz noun meaning "short, free improvised passage performed by the whole band" dates from 1929, and yielded jam session (1933); perhaps from jam (n.) in sense of "something sweet, something excellent." Noun sense of "machine blockage" is from 1890, which probably led to the colloquial meaning "predicament," first recorded 1914.
jam (n.): "fruit preserve," 1730s, probably a special use of jam (v.) with a sense of "crush fruit into a preserve."
Jamaica: West Indian island, from Taino (Arawakan). The Jamaica in New York probably is a Delaware (Algonquian) word meaning "beaver pond" alt. by infl. of the island name.
jamb: 1334, from O.Fr. jambe "pier, side post of a door," originally "a leg, shank," from L.L. gamba "leg, (horse's) hock" (see gambol).
jambalaya: 1872, from Louisiana Fr., from Prov. jambalaia "stew of rice and fowl."
jamboree: 1868, Amer.Eng., perhaps from jam (n.) on pattern of shivaree. For the second element, Weekley suggestsFr. bourree, a kind of rustic dance. Klein thinks the whole thing is of Hindu origin. Name given to 1920 International Rally of Boy Scouts, and used subsequently by them.
James: masc. proper name, name of two of Christ's disciples, late 12c. M.E. vernacular form of L.L. Jacomus (cf. O.Fr. James, Sp. Jaime, It. Giacomo), altered from L. Jacobus (see Jacob). The Welsh form was Iago, the Cornish Jago.
Jamesian: "of or in the mode of James," 1875 in ref. to William James (1842-1910) U.S. philosopher and exponent of pragmatism; 1905 in ref. to his brother Henry James (1843-1916), U.S. expatriate novelist.
jams: 1966, abstracted from pajamas (q.v.).
Jane: fem. proper name, from Fr. Jeanne, O.Fr. Jehane, from M.L. Johanna (see John). As a generic name for "girl, girlfriend" it is attested from 1906 in U.S. slang. Never a top-10 list name for girls born in the U.S., it ranked in the top 50 from 1931 to 1956. It may owe its "everywoman" reputation to its association with John.