Online Etymology Dictionary

jargon (n.): mid-14c., "unintelligible talk, gibberish; chattering, jabbering," from Old French jargon "a chattering" (of birds), also "language, speech," especially "idle talk; thieves' Latin" (12c.). Ultimately of echoic origin (compare Latin garrire "to chatter").

From 1640s as "mixed speech, pigin;" 1650s as "phraseology peculiar to a sect or profession," hence "mode of speech full of unfamiliar terms." Middle English also had it as a verb, jargounen "to chatter" (late 14c.), from French.
jarhead (n.): also jar-head, "U.S. Marine," by 1985 (but in a biographical book with a World War II setting), from jar + head (n.). Also used as a general term of insult (by 1979) and by 1922 as a Georgia dialectal word for "mule."
jarl (n.): "nobleman," especially a Norse or Danish chieftain, from Old Norse jarl (see earl).
jarring (adj.): "having a sharp, unpleasant effect," 1550s, present-participle adjective from jar (v.). Related: Jarringly.
jasmine (n.): 1570s, from French jasmin (Middle French jessemin, 16c.), from Arabic yas(a)min, from Persian yasmin (compare Greek iasme, iasmelaion, name of a Persian perfume which was perhaps oil of jasmine). The plant first was grown in England 16c. The forms in other Germanic languages also are from French.
Jason: masc. proper name, from Greek Eason, from Hebrew Yehoshua, a common name among Hellenistic Jews (see Joshua). In Greek mythology, son of Aeson, leader of the Argonauts, from Latin Jason, from Greek Iason, perhaps related to iasthai "to heal" (see -iatric). The names were somewhat merged in Christian Greek.
jasper (n.): precious stone, c. 1300, from Anglo-French jaspre, Old French jaspre, with excrescent -r-, a variant of jaspe (12c.), from Latin iaspidem (nominative iaspis), from Greek iaspis "jasper," via an Oriental language (compare Hebrew yashpeh, Akkadian yashupu). The modern use of the word is more restricted than in ancient times. Hence, from French, jaspé (1851 in English) "mottled or variegated like jasper."
Jasper: masc. proper name, English form of Caspar or of Gaspar, the traditional name of one of the Three Kings. Said by Klein to be of Persian origin and meaning literally "treasure-holder." Used from 1896 for "a rustic simpleton."
jaundice (n.): "morbid condition characterized by yellowish skin and eyes (caused by bile pigments in the blood)," c. 1300, jaunis, from Old French jaunice, earlier jalnice, "yellowness" (12c.), from jaune/jalne "yellow," from Latin galbinus "greenish yellow" (also source of Italian giallo), extended form of galbus, which probably is from PIE *ghel- "yellow, green" (see Chloe). With intrusive -d- (compare sound (n.1)).

Figurative meaning "feeling in which views are colored or distorted" first recorded 1620s, from yellow's association with bitterness and envy (see yellow (adj.)). In Old English geolu adl "yellow sickness;" in Middle English also gulesought.
jaundice (v.): "to affect with prejudice or envy," 1791, but usually in figurative use. Related: Jaundiced.
jaunt (n.): 1670s in modern sense of "short pleasure trip," earlier "tiresome journey" (1590s), from jaunt (v.).
jaunt (v.): "tire (a horse) by riding back and forth on it, ride hard," 1560s, of unknown origin, "the word being confused with other words of similar or related meanings" [Century Dictionary]. Not found in Middle English, perhaps from some obscure French word. Also "be jolted or shaken up" (1570s), main modern sense "wander here and there for pleasure" is from 1640s. Related: Jaunted; jaunting.
jaunty (adj.): also janty, jantee, etc., 1660s, "elegant, stylish," an imperfect or jocular attempt to render into English the contemporary pronunciation of French gentil "nice, pleasing," in Old French "noble" (see gentle). Meaning "easy and sprightly in manner" first attested 1670s. The same French word otherwise was Englished as genteel. Related: Jauntily; jauntiness.
java (n.): "coffee," 1850, short for Java coffee (1787), originally a kind of coffee grown on Java and nearby islands of modern Indonesia. By early 20c. it meant coffee generally. The island name is shortened from Sanskrit Yavadvipa "Island of Barley," from yava "barley" + dvipa "island." Related: Javan (c. 1600); Javanese (1704).
javelin (n.): late 15c., from Middle French javeline (15c.), fem. diminutive of Old French javelot "a spear" (12c.), probably from Gaulish or another Celtic source (compare Old Irish gabul "fork;" Welsh gafl "fork," gaflach "feathered spear"), from Celtic *gablakko-, from PIE *ghabholo- "a fork, branch of a tree." Also found in Italian (giavelotto) and Middle High German (gabilot). Javelot itself was borrowed in Middle English (mid-15c.), but this is the form of the word that has endured.
javelot (n.): "small spear," mid-15c.; see javelin.
jaw (n.): late 14c., jowe, joue, "the bones of the mouth," "A word of difficult etymology" [OED]. Probably from Old French joue "cheek," originally jode, from Gallo-Romance *gauta or directly from Gaulish *gabata, but there are phonetic problems; or perhaps a variant of Germanic words related to chew (v.); compare also the two nouns jowl. Replaced Old English ceace, ceafl. Jaws as "holding and gripping part of an appliance" is from mid-15c.; figuratively, of time, death, defeat, etc., from 1560s.
jaw (v.): 1610s, "to catch in the jaws, devour," from jaw (n.). In slang from 1748, "to gossip, to speak;" 1810 as "to scold." Related: Jawed; jawing. Hence 19c. U.S. slang jawsmith "talkative person; loud-mouthed demagogue" (1887), nautical slang jaw-tackle "the mouth" (1829), and the back-formed colloquial noun jaw "rude talk, abusive clamor" (1748).
jaw-breaker (n.): also jawbreaker 1810, "word hard to pronounce" (jawbreakingly, in reference to pronouncing words, is from 1824), from jaw (n.) + agent noun from break (v.). As a type of hard candy, by 1911.
jaw-jaw (n.): "long pointless talking," 1958, from earlier verb meaning "talk tediously" (1831), from reduplication of jaw in a colloquial sense (see jaw (v.)). Related: Jaw-jawing.
jawbone (n.): also jaw-bone, mid-15c., from jaw (n.) + bone (n.). Hence jawboning "lecturing, hectoring" (1966), a term associated with the U.S. presidential administration of Lyndon Johnson; compare jaw (v.).
jay (n.): the common European jay (Garrulus glandarinus), early 14c. (late 12c. as a surname), from Old North French gai, Old French jai "magpie, jay" (12c., Modern French geai), from Late Latin gaius "a jay," probably echoic of the bird's harsh warning cry and supposedly influenced by Latin Gaius, a common Roman proper name.

For other bird names from proper names, compare martin and parrot. Applied to the North American blue jay (Cyanocitta cristata) from 1709; it is unrelated but has similar vivid markings, is noisy and restless, and also has a harsh call. Applied to humans in sense of "impertinent chatterer, loud, flashy dresser" from 1520s. Jolly as a jay was a Middle English expression for "very happy, joyful."
jay (adj.): "fourth-rate, worthless" (as in a jay town), 1888, American English, earlier as a noun, "hick, rube, dupe" (1884); apparently from some disparaging sense of jay (n.). Perhaps via a decaying or ironical use of jay in the old slang sense "flashy dresser." Century Dictionary (1890s) notes it as actors' slang for "an amateur or poor actor" and as an adjective a general term of contempt for audiences.
"A jay hasn't got any more principle than a Congressman. A jay will lie, a jay will steal, a jay will deceive, a jay will betray; and, four times out of five, a jay will go back on his solemnest promise. The sacredness of an obligation is a thing which you can't cram into no blue-jay's head." [Mark Twain, "Blue-Jays"]
They were said to be disliked by hunters because their cries aroused deer. Barrère and Leland's "Dictionary of Slang, Jargon & Cant" [1889] describes the noun as an American term of contempt for a person, "a sham 'swell;' a simpleton," and suspect it might be from jayhawker.
jay-bird (n.): also jaybird, 1660s, from jay (n.) "the common jay" + bird (n.). It appears after jay (n.) began to be used of persons, too.
Jaycee (n.): 1937, American English, acronym from pronunciation of J.C. (pronounced "jay-cee"), abbreviation of Junior Chamber (of Commerce).
jayhawker (n.): "freebooter, guerrilla," American English, 1858, originally "irregular or marauder during the 'Bleeding Kansas' troubles" (especially one who came from the North). It seems to have come into widespread use only during the Civil War. There was said to have been a bird of this name, but evidence for it is wanting. Perhaps a disparaging use from jay (n.). Hence back-formed verb jayhawk "harass" (1866).
Bushwhackers are men, united together, but not soldiers, who live in the bush; and whose avowed object is to kill every Union soldier they can, and cripple, so far as they can, the resources of the Federal military power. The jayhawkers are thieves. They plunder indiscriminately from all parties. In the same band are both rebel and Union men. ... Guerilla bands are companies enlisted and sworn into the rebel service; but not belonging to the armies. [Henry M. Painter, "Brief Narrative of Incidents in the War in Missouri," Boston, 1863.]
jaywalking (n.): by 1912, American English (said in original citation to be a Kansas City term), from jay, perhaps with notion of boldness and impudence. Related: Jaywalk; jaywalker.
jazz (n.): by 1912, American English, first attested in baseball slang; as a type of music, attested from 1913. Probably ultimately from Creole patois jass "strenuous activity," especially "sexual intercourse" but also used of Congo dances, from jasm (1860) "energy, drive," of African origin (compare Mandingo jasi, Temne yas), also the source of slang jism.
If the truth were known about the origin of the word 'Jazz' it would never be mentioned in polite society. ["Étude," Sept. 1924]
Meaning "rubbish, unnecessary talk or ornamentation" is from 1918. Slang all that jazz "et cetera" first recorded 1939.
jazz (v.): "to speed or liven up," 1917, from jazz (n.). Related: jazzed; jazzing.
Jazz Age: 1921; see jazz (n.); popularized 1922 in writings of F. Scott Fitzgerald; usually regarded as the years between the end of World War I (1918) and the Stock Market crash of 1929.
We are living in a jazz age of super-accentuated rhythm in all things; in a rhythm that (to "jazz" a word) is super-normal, a rhythm which is the back-flare from the rhythm of a super war. ["Jacobs' Band Monthly," Jan. 1921]
jazzbo (n.): 1917, "low, vulgar jazz," from jazz (n.). Later in 20c. it was in use as a derogatorty term for persons, especially blacks.
jazzed (adj.): "made more lively or colorful," 1919, past participle adjective from jazz (v.).
Jazzercise (n.): 1977, originally a proprietary name, from jazz (n.) + ending from exercise.
jazzetry (n.): "poetry reading accompanied by jazz music," 1959, from jazz (n.) + poetry.
jazzman (n.): 1917, from jazz (n.) + man (n.).
jazzy (adj.): "resembling jazz music, spirited, lively, exciting," 1918, from jazz (n.) + -y (2). Related: Jazzily; jazziness.
je ne sais quoi (n.): "an inexpressible something," French, literally "I do not know what."
[T]hey are troubled with the je-ne-scay-quoy, that faign themselves sick out of niceness but know not where their own grief lies, or what ayls them. [Thomas Blount, "Glossographia," 1656]
jealous (adj.): c. 1200, gelus, later jelus, "possessive and suspicious," originally in the context of sexuality or romance (in any context from late 14c.), from Old French jalos/gelos "keen, zealous; avaricious; jealous" (12c., Modern French jaloux), from Late Latin zelosus, from zelus "zeal," from Greek zelos, which sometimes meant "jealousy," but more often was used in a good sense ("emulation, rivalry, zeal"), from PIE root *ya- "to seek, request, desire" (see zeal). In biblical language (early 13c.) "tolerating no unfaithfulness." Also in Middle English sometimes in the more positive sense, "fond, amorous, ardent" (c. 1300) and in the senses that now go with zealous, which is a later borrowing of the same word, from Latin.
Most of the words for 'envy' ... had from the outset a hostile force, based on 'look at' (with malice), 'not love,' etc. Conversely, most of those which became distinctive terms for 'jealousy' were originally used also in a good sense, 'zeal, emulation.' [Buck, pp.1138-9]
Among the ways to express "jealous" in other tongues are Swedish svartsjuka, literally "black-sick," from phrase bara svarta strumpor "wear black stockings," also "be jealous." Danish skinsyg "jealous," literally "skin-sick," is from skind "hide, skin" said to be explained by Swedish dialectal expression fa skinn "receive a refusal in courtship."
jealously (adv.): late 14c., "in a zealous manner;" 1718, "in a suspicious and possessive manner," from jealous + -ly (2).
jealousy (n.): c. 1200 in reference to sexual possessiveness and suspicion, from Old French jalousie "enthusiasm, love, longing; jealousy" (12c.), from jalos "keen, zealous; avaricious; jealous" (see jealous). Also sometimes in Middle English in a sense "solicitude, carefulness, regard," the connecting notion being "watchfulness." Meaning "zeal, fervor, devotion" is from late 14c.
Jean: masc. proper name, French equivalent of John (q.v.). The fem. proper name is from the French equivalent of Jane. Related: Jeanette.
jean (n.): "twilled cotton cloth," mid-15c., Geayne, short for Gene fustian, from Middle French jean fustian "fustian (a type of twilled cotton cloth) of Genoa," the Italian city, from Old French Jannes "Genoa," from Latin Genua (see Genoa). Compare obsolete jane, name of a small silver coin of Genoa that circulated in England 15c. The plural form jeans became standard by mid-19c. In the sense "trousers made of jeans" it is attested by 1908; noted as characteristic of teenagers from 1959. Not originally blue.
After sheep could be protected from the wolves, the people fared better in the matter of clothing. Flannel and linsey were woven for the wear of women and children, while jeans was woven for the men. For want of other dye-stuffs, the wool for the jeans was almost invariably colored with the bark or young shoots of the walnut; hence the inevitable "butternut" worn so extensively in the West for many years. ["History of Menard and Mason Counties, Illinois," 1879]
jeans (n.): see jean.
Jedi (n.): characters in the "Star Wars" sagas, 1977, apparently an invented word.
jeep (n.): early 1941, American English military slang, acronym from G.P., abbreviation of General Purpose (car), but certainly influenced by Eugene the Jeep (who had extraordinary powers but said only "jeep"), from E.C. Segar's comic strip "Thimble Theater" (home of Popeye the Sailor). Eugene the Jeep first appeared in the strip March 13, 1936. The vehicle was in development from 1940, and the Army planners' initial term for it was light reconnaissance and command car.
jeepers (interj.): 1900, American English, euphemistic alteration of Jesus.
jeer (v.): 1550s, gyr, "deride, to mock," of uncertain origin; perhaps from Dutch gieren "to cry or roar," or Middle Dutch scheeren or German scheren "to plague, vex," literally "to shear" (as a mark of contempt or disgrace). OED finds the suggestion that it is an ironical use of cheer "plausible and phonetically feasible, ... but ... beyond existing evidence." Related: Jeered; jeering.
jeer (n.): "a scoff, a taunt," 1620s, from jeer (v.).
Jeeves: personification of the perfect valet, 1930, from character in P.G. Wodehouse's novels. The surname is attested from 1120, perhaps from a pet form of Genevieve.
jeez (interj.): minced oath, also jeeze, 1922, American English, euphemistic corruption of Jesus.