Online Etymology Dictionary

J: 10th letter of the English alphabet, pronounced "jay," as in "kay" for -k-, but formerly written out as jy, rhyming with -i- and corresponding to French ji.

one of the most stable English letters (it has almost always the same sound), it is a latecomer to the alphabet and originally had no sound value. The letter itself began as a scribal modification of Roman -i- in continental Medieval Latin. The scribes added a "hook" to small -i-, especially in the final position in a word or roman numeral, to distinguish it from the strokes of other letters. The dot on the -i- (and thus the -j-) and the capitalization of the pronoun I are other solutions to the same problems.

In English, -j- was used as a roman numeral throughout Middle English, but the letter -y- was used to spell words ending an "i" sound, so -j- was not needed to represent a sound. Instead, it was introduced into English c. 1600-1640 to take up the consonantal sound that had evolved from the Roman i- since Late Latin times. In Italian, g- was used to represent this, but in other languages j- took the job. This usage is attested earliest in Spanish, where it was in place before 1600.
No word beginning with J is of Old English derivation. [OED]
English dictionaries did not distinguish words beginning in -i- and -j- until 19c., and -j- formerly was skipped when letters were used to express serial order.

In Latin texts printed in modern times, -j- often is used to represent Latin -i- before -a-, -e-, -o-, -u- in the same syllable, which in Latin was sounded as the consonant in Modern English you, yam, etc., but the custom has been controversial among Latinists:
The character J, j, which represents the letter sound in some school-books, is an invention of the seventeenth century, and is not found in MSS., nor in the best texts of the Latin authors. [Lewis]
In English words from Hebrew, -j- represents yodh, which was equivalent to English consonantal y (hence hallelujah) but many of the Hebrew names later were conformed in sound to the modern -j- (compare Jesus).
j'accuse: French, literally "I accuse," a phrase made famous by Emile Zola in a public letter (published Jan. 13, 1898) attacking the irregularities of the Dreyfus trial.
jab (v.): 1813, "to thrust or strike with a point," a Scottish variant of job "to strike, pierce, thrust," from Middle English jobben "to jab, thrust, peck" (c. 1500), a word of unknown origin, perhaps imitative. Related: Jabbed; jabbing.
jab (n.): 1825, "a thrust or poke with the point of something," from jab (v.). Meaning "a punch with the fist" is from 1889. Sense of "injection with a hypodermic needle," once beloved by newspaper headline writers, is from 1914.
jabber (v.): "talk rapidly and indistinctly," 1650s, spelling variant of Middle English jablen (c. 1400), also javeren, jaberen, chaveren, jawin; probably ultimately echoic. Related: Jabbered; jabbering. The noun, "rapid, unintelligible talk" is 1727, from the verb. Related: Jabberment (Milton).
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.
jabot (n.): 1823, "frill of a men's shirt," from French jabot "gizzard (of a bird), frill on a shirt front" (16c.), a word of unknown origin. Klein suggests a connection with gaver "to cram, gorge," and thus ultimately with English jaw (n.). Of women's clothing from 1869.
jabroni (n.): c. 2000, professional wrestling slang for one whose main purpose is to make the better-known wrestlers of the organization look good; he or she does this by losing to them. More commonly known as a jobber, in a specialized sense of that word (though some enthusiasts claim there is a difference), and perhaps a mock-Italianized form of that word (but compare jaboney "naive person; immigrant; hoodlum," a word of unknown origin, in American English use c. 1990).
Jobber -- A performer who regularly loses on television and doesn't receive much if any push. A comparable term for such a performer is jabroni, which is a favorite catch-phrase of Dwayne "The Rock" Johnson. To soften the blow of such labels, some wrestling promotions refer to jobbers as enhancement talent. Carpenter was the phrase used by earlier generations. ["The Professional Wrestlers' Instructional and Workout Guide," 2005]
jacaranda (n.): tropical American tree, 1753, from Portuguese jacarandá, from Tupi yacaranda.
jacinth (n.): c. 1200, a blue gem (occasionally a red one), from Old French jacinte, iacinte "hyacinth; jacinth," or directly from Late Latin iacintus (see hyacinth). In modern use, a reddish-orange gem. The word is hyacinth with the h- lost and the initial -i- made consonantal.
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."
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."
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."
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-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.
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.
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.
jack-knife (v.): 1776, "to stab," from jack-knife (n.). Intransitive meaning "to fold or bend" the body is said to date from the time of the American Civil War. The truck accident verbal sense is from 1949. Related: Jackknifed; jackknifing.
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.
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).
jack-shit (n.): "nothing at all," 1968, U.S. slang, from jack (n.) + shit (n.).
jackal (n.): c. 1600, from French chacal, earlier jackal, from Turkish çakal, from Persian shaghal, from or cognate with Sanskrit srgala-s, literally "the howler." Figurative sense of "skulking henchman" is from the old belief that jackals stirred up game for lions.
jackanapes (n.): mid-15c., "a monkey," also "an impertinent, conceited fellow, an absurd fop," a general term of reproach (in mid-15c. especially a contemptuous nickname for William de la Pole, Duke of Suffolk), of unknown origin. Apparently from Jack of Naples, but whether this is some specific personification of Jack (which is attested from 16c. as "saucy or impertinent fellow") or folk etymology of jack (n.) + ape (n.) is unknown. See extensive note in OED. Century Dictionary suggests "orig., it is supposed, a man who exhibited performing apes." Farmer & Henley say "originally, no doubt, a gaudy-suited and performing ape." Its fem. counterpart is Jane-of-apes (Massinger) "a pert, forward girl."
jackaroo (n.): Australian for "a new arrival from Britain," 1867, from Jack + ending from kangaroo. The female counterpart jillaroo is attested from 1945.
jackass (n.): "male ass," 1727, from jack (n.) + ass (n.1). Contemptuous meaning "stupid person" is attested from 1823. Related: Jackassism (1837, American English); jackassery (1833).
jackboot (n.): also jack-boot, 1680s, type of large, strong over-the-knee cavalry boot of 17c.-18c., later a type worn by German military and para-military units in the Nazi period. From jack (n.), though the exact sense here is unclear + boot (n.1). Figurative of military oppression since 1768. Related: Jackbooted.
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.
jacket (n.): mid-15c., "short garment for men," from Old French jaquet "short coat with sleeves," diminutive of jaque, a kind of tunic, which is of uncertain origin. Probably it is from Jacque, the male proper name, also the generic name of a French peasant (see jacquerie) with extended material senses as in native jack (n.). But possibly it is from or influenced by jaque (de mailles) "short, tight-fitting coat," originally "coat of mail," from Spanish jaco, from Arabic shakk "breastplate." Meaning "paper wrapper of a book" is first attested 1886.

Iakke, jakke "a short, close-fitting stuffed or quilted tunic, often serving as a defensive garment" is attested in English from late 14c. (from Old French jaque), and by c. 1400 was being used for "woman's short tunic." It is possible that jacket was formed in English as a diminutive of this.
jackpot (n.): also jack-pot, "big prize," 1944, from slot machine sense (1932), from now-obsolete poker sense (1881) in reference to antes that begin when no player has a pair of jacks or better; from jack (n.) in the card-playing sense + pot (n.1). Earlier, in criminal slang, it meant "trouble," especially "an arrest" (1902).
The regular Draw-Poker game is usually varied by occasional Jack-Pots, which are played once in so many deals, or when all have refused to play, or when the player deals who holds the buck, a marker placed in the pool with every jack-pot. In a jack-pot each player puts up an equal stake and receives a hand. The pot must then be opened by a player holding a hand of the value of a pair of knaves (jacks) or better. If no player holds so valuable a hand the deal passes and each player adds a small sum to the pot or pool. When the pot is opened the opener does so by putting up any sum he chooses, within the limit, and his companions must pay in the same amount or "drop." They also possess the right to raise the opener. The new cards called for are then dealt and the opener starts the betting, the play proceeding as in the regular game. ["Encyclopaedia Britannica," 11th ed., 1911, "Poker." The article notes "Jack-Pots were introduced about 1870."]
To hit the jackpot "be very successful" is from 1938.
jacks (n.): dexterity game played with a ball and small objects, 1900, from earlier jackstone "small round pebble used in games" (1792), which seems to be an alteration of checkstone (1745). The metal pieces with five arms or tines, made to be used in the game, are so called from 1908.
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].
jackstraw (n.): 1590s, "effigy of a man made of straw," from Jack + straw (n.); hence "man without substance or means." It also was a name of one of the leaders of the Peasants' Revolt of 1381. As the name of a game played with straw or strips, from 1801. Related: Jackstraws.
Jacob: masc. proper name; Old Testament patriarch, son of Isaac and Rebecca and father of the founders of the twelve tribes, from Late Latin Iacobus, from Greek Iakobos, from Hebrew Ya'aqobh, literally "one that takes by the heel; a supplanter" (Gen. xxviii:12), a derivative of 'aqebh "heel." The most popular name for boys born in the U.S. from 1999 through 2008. Jacob's ladder, in various transferred uses from 1733, is from Gen. xxviii:12. In Spanish as Jago, Iago, also Diego; with alterations as Italian Giacomo, James, and (contracted) Spanish Jaime.
Jacobean (adj.): also Jacobian, 1770, literally "of James" (king or apostle), later (1844) especially "of the literary and architectural style of the time of James I," king of England 1603-1625. Supporters of James II after his abdication were called Jacobites (1689).
Jacobin (n.): early 14c., "Dominican friar," from Old French Jacobin (13c.) "Dominican friar" (also, in the Middle East, "a Copt"); so called because the order built its first convent near the church of Saint-Jacques in Paris. The masc. proper name Jacques is from Late Latin Iacobus, for which see Jacob.

The Revolutionary extremists ("Society of the Friends of the Constitution") made their club headquarters there October 1789 and supported Robespierre during the Terror. They were suppressed along with him in November 1794 and many members executed. In English, the word quickly became a scare-word for the worst excesses of the French Revolution, and since 1793 it has been used generically and often inappropriately of allegedly radical politicians and reformers. Related: Jacobinism; Jacobinic; Jacobinical.
Jacquard (adj.): in reference to a type of loom, 1841, from Joseph Marie Jacquard (1752-1834) of Lyons, inventor of new weaving technology c. 1800.
Jacquerie (n.): "French peasantry," 1520s, from Middle 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).
Jacuzzi (n.): type of whirlpool bath, 1961, U.S. proprietary name, from Jacuzzi Bros. Inc., Little Rock, Arkansas, who earlier made jet pumps for motorboats.
jade (n.1): ornamental stone, 1721, earlier iada (1590s), from French le jade, misdivision of earlier l'ejade, from Spanish piedra de (la) ijada or yjada (1560s), "(stone of) colic or pain in the side" (jade was thought to cure this), from Vulgar Latin *iliata, from Latin ileus "severe colic" (see ileus). As an adjective from 1865.
jade (n.2): "worn-out horse," late 14c., apparently originally "cart horse," a word of uncertain origin. Barnhart and Century Dictionary suggests a variant of yaid, yald "whore," literally "mare" (c. 1400), from a Scandinavian source akin to Old Norse jalda "mare," and ultimately from Finno-Ugric (compare Mordvin al'd'a "mare"). But OED finds the assumption of a Scandinavian connection "without reason." As a term of abuse for a woman, it dates from 1550s; in early use also of mean or worthless men, and sometimes simply "a young woman."
jade (v.): "to weary, tire out, make dull," c. 1600, from jade (n.2). Related: Jaded; jading.
jaded (adj.): "bored by continual indulgence," 1630s; past participle adjective from jade (v.). Related: Jadedly; jadedness.
jag (n.1): "period of unrestrained activity," 1887, American English, perhaps via intermediate sense of "as much drink as a man can hold" (1670s), from earlier meaning "load of hay or wood" (1590s), of unknown origin. Used in U.S. colloquial speech from 1834 to mean "a quantity, a lot."
jag (n.2): "slash or rend in a garment," c. 1400, of unknown origin.
jager (n.): also jaeger, "German sharpshooter," 1776, from German jäger, literally "huntsman," from jagen "to hunt," from Old High German jagon, related to Old Frisian jagia, Dutch jagen "to hunt," Old Norse jaga "to drive, to move to and fro" (see yacht (n.)). Applied to riflemen and sharpshooters in the German and Austrian armies. Englished as yager, yaeger from 1804.
jagged (adj.): mid-15c., "having notches," from verb jaggen (c. 1400) "to pierce, slash, cut; to notch or nick; cut or tear unevenly," a Scottish and northern English word of unknown origin, related to jag (n.2). Originally of garments with regular "toothed" edges; meaning "with the edge irregularly cut" is from 1570s. Related: Jaggedly; jaggedness.
jaguar (n.): big spotted cat of the Americas (Felis onca), c. 1600, from Portuguese jaguar, from Tupi jaguara, said in old sources to denote any large beast of prey ["tygers and dogs," in Cullen's translation of Abbe Clavigero's "History of Mexico"]. Compare Tupi jacare "alligator." As a type of stylish British-made car from 1935; in this sense the abbreviation Jag is attested from 1959.
Jah (n.): 1530s, a form of Hebrew Yah, short for Yahweh "Jehovah" (see Yahweh; also see J). Used in some English bibles. Cognate with the second element in hallelujah and in Elijah.
jai alai (n.): 1902, American English, originally in a Cuban context, from Basque, from jai "celebration" + alai "merry."
jail (n.): c. 1300 (c. 1200 in surnames) "a jail, prison; a birdcage." The form in j- is from Middle English jaile, from Old French jaiole "a cage; a prison," from Medieval Latin gabiola "a cage," from Late Latin caveola, diminutive of Latin cavea "a cage, enclosure, stall, coop; a hollow place, a cavity" (see cave (n.)).

The form in g- was the more usual in Middle English manuscripts (gaile, also gaiole), from Old French gaiole "a cage; a prison," a variant spelling that seems to have been frequent in Old North French, which would have been the system familiar to Norman scribes. Now pronounced "jail" however it is spelled. Persistence of gaol (preferred in Britain) is "chiefly due to statutory and official tradition" [OED], and, probably, the fact that it is known the Americans spell it the other way.

In U.S. usually a place of confinement for petty offenders. The Medieval Latin word also is the source of Spanish gayola, Italian gabbiula.