Online Etymology Dictionary

gaseous (adj.): "in the form of a gas," 1799, from gas (n.) + -ous. Related: Gaseousness.
gash (n.): 1540s, alteration of Middle English garce "a gash, cut, wound, incision" (early 13c.), from Old North French garser "to scarify, cut, slash" (Old French *garse), apparently from Vulgar Latin *charassare, from Greek kharassein "engrave, sharpen, carve, cut," from PIE *gher- (4) "to scrape, scratch" (see character). Loss of -r- is characteristic (see ass (n.2)). Slang use for "vulva" dates to mid-1700s. Provincial English has a set of words (gashly, gashful, etc.) with forms from gash but senses from gast- "dreadful, frightful."
gash (v.): 1560s, alteration of older garsh, from Middle English garsen (late 14c.), from Old North French garser "to cut, slash" (see gash (n.)). For loss of -r-, see ass (n.2). Related: Gashed; gashing.
gasket (n.): 1620s, caskette, originally nautical, "small rope or plaited coil" used to secure a furled sail, of uncertain origin, perhaps from French garcette "a gasket," literally "little girl, maidservant," diminutive of Old French garce "young woman, young girl; whore, harlot, concubine" (13c.), fem. of garçon (see garcon). Century Dictionary notes Spanish garcette "a gasket," also "hair which falls in locks." Machinery sense of "packing (originally of braided hemp) to seal metal joints and pistons" first recorded 1829.
gasohol (n.): gasoline and ethanol mixture, 1975, from gasoline + (ethyl) alcohol.
gasoline (n.): "lightest volatile liquid obtained from distillation of petroleum," 1864 (alternative spelling gasolene is from 1865), from gas (n.) + -ol (probably here representing Latin oleum "oil") + chemical suffix -ine (2). Shortened form gas was in common use in U.S. by 1897. Gas station as a fuel filling station for automobiles recorded by 1924.
gasometer (n.): 1790, from gas (n.1) + -meter. Originally an instrument for measuring gasses; as this also involves collecting and storing them, it came also to be used for "a storehouse for gas." Related: Gasometric; gasometry.
gasp (v.): late 14c., gaspen, "open the mouth wide; exhale," of uncertain origin, perhaps from Old Norse geispa "to yawn," or its Danish cognate gispe "gasp," which probably are related to Old Norse gapa "open the mouth wide" (see gap (n.)). Related: Gasped; gasping.
gasp (n.): 1570s, from gasp (v.). Earliest attested use is in the phrase last gasp "final breath before dying." To gasp up the ghost "die" is attested from 1530s.
gassy (adj.): 1757, from gas (n.1) + -y (2). Related: Gassily; gassiness.
gast (adj.): "animal which does not produce in season," 1729, an East Anglian dialect word, perhaps from or related to Middle Dutch gast "barren soil."
gastrectomy (n.): 1881, from gastro- "stomach" + -ectomy "a cutting out."
gastric (adj.): 1650s, from Modern Latin gastricus, from Greek gaster (genitive gastros) "stomach, paunch, belly," often figurative of gluttony or greed, also "womb, uterus; sausage," by dissimilation from *graster, literally "eater, devourer," from gran "to gnaw, eat," from PIE root *gras- "to devour" (source also of Greek grastis "green fodder," Latin gramen "fodder, grass," Old English cærse "cress").
gastritis (n.): 1806, medical Latin, from gastro- "stomach" + -itis "inflammation." Coined by French pathologist François-Boissier de la Croix de Sauvages (1706-1767).
gastro-: also gastero-, scientific word-forming element meaning "stomach," before vowels gastr-, from Greek gastro-, comb. form of gaster (genitive gastros) "belly, paunch; womb" (see gastric). Also used in compounds in ancient Greek, as gastrobarys "heavy with child."
gastro-enteritis (n.): also gastroenteritis, 1823, from gastro- + enteritis. Related: Gastro-enteric.
gastro-enterology (n.): also gastroenterology, 1904, from gastro- + enterology, from Greek enteron "an intestine, piece of gut" (see enteric). Related: Gastroenterologist.
gastro-intestinal (adj.): also gastrointestinal, 1821, from gastro- + intestinal.
gastrocnemius (n.): 1670s, from Latinized form of Greek gastroknemia "calf of the leg," from gaster "belly" (see gastric) + kneme "calf of the leg," from PIE *kone-mo- "shin, leg-bone" (see ham (n.1)). So called for its form (the "protuberant" part of the calf of the leg). Related: Gastrocnemical.
gastrolator (n.): "belly-worshipper; one whose god is his own belly," 1690s, from gastro- + Greek -latros "serving" (see -latry). Perhaps modeled on French gastrolatre. Related: Gastrolatrous.
gastrolith (n.): 1854, from German Gastrolith (by 1843) or Modern Latin gastrolithus, from gastro- "stomach" + -lith "stone."
gastrology (n.): "cooking, good eating," 1810, from gastro- "stomach" + -logy. Compare gastronomy. Gastrologia was the title of a lost work by Archestratus.
gastronome (n.): "a judge of the arts of cookery," 1823, from French gastronome, a back-formation from gastronomie (see gastronomy). Alternative gastronomer is recorded from 1820.
gastronomic (adj.): 1817, from French gastronomique, from gastronomie (see gastronomy). Related: Gastronomical; gastronomically.
gastronomy (n.): 1814, from French gastronomie, coined 1800 by Joseph de Berchoux (1762-1838) as title of poem on good living, after Gastrologia, title of a now-lost poem of antiquity, quoted by Athenaeus (see gastrology). Berchoux's word is from gaster + nomos "arranging, regulating" (from nemein "manage;" see numismatic). Related: Gastronomer.
gastropod (n.): 1826, gasteropod (spelling without -e- by 1854), from Modern Latin Gasteropoda, name of a class of mollusks, from Greek gaster (genitive gastros) "stomach" (see gastric) + pous (genitive podos) "foot," from PIE root *ped- (1) "a foot" (see foot (n.)). From the ventral position of the mollusk's "foot."
gastrula (n.): 1874, a Modern Latin coinage (Haeckel), from Latin gaster, from Greek gaster (genitive gastros) "stomach" (see gastric) + Latin -ula, diminutive suffix. Related: Gastrular; gastrulation.
gat (n.): "revolver," 1904, slang shortening of Gatling (gun); by 1880, gatlin was slang for a gun of any sort.
gate (v.): "provide with a gate," 1906, from gate (n.). Originally of moulds. Related: Gated (1620s). Gated community recorded by 1989 (earliest reference to Emerald Bay, Laguna Beach, Calif.).
gate (n.): "opening, entrance," Old English geat (plural geatu) "gate, door, opening, passage, hinged framework barrier," from Proto-Germanic *gatan (source also of Old Norse gat "opening, passage," Old Saxon gat "eye of a needle, hole," Old Frisian gat "hole, opening," Dutch gat "gap, hole, breach," German Gasse "street, lane, alley"), of unknown origin. Meaning "money collected from selling tickets" dates from 1896 (short for gate money, 1820). Gate-crasher is from 1926 as "uninvited party guest;" 1925 in reference to motorists who run railway gates. Finnish katu, Lettish gatua "street" are Germanic loan-words.
gate-house (n.): also gatehouse, "house for a gatekeeper," late 14c., from gate (n.) + house (n.).
gate-keeper (n.): also gatekeeper, 1570s, from gate (n.) + keeper. Figurative use by 1872.
gateau (n.): 1845, from French gâteau "cake," from Old French gastel, from Frankish *wastil "cake," from Proto-Germanic *was-tilaz, from PIE *wes- (5) "to eat, consume."
gateway (n.): "passage, entrance," 1707, from gate (n.) + way (n.). Figurative use from 1842.
gather (v.): Old English gadrian, gædrian "unite, agree, assemble; gather, collect, store up" (transitive and intransitive), used of flowers, thoughts, persons; from Proto-Germanic *gaduron "come or bring together, unite" (source also of Old English gæd "fellowship, companionship," gædeling "companion;" Middle Low German gadderen; Old Frisian gaderia; Dutch gaderen "to gather," gade "spouse;" German Gatte "husband;" Gothic gadiliggs), from PIE *ghedh- "to unite, join" (see good (adj.)). Change of spelling from -d- to -th- is 1500s, reflecting earlier change in pronunciation (as in mother, weather, father). Related: Gathered; gathering.
gather (n.): "plait or fold in cloth," 1660s, from gather (v.).
gatherer (n.): c. 1200, agent noun from gather.
gathering (n.): mid-12c., gadering, "an assembly of people, act of coming together," from late Old English gaderung "a gathering together, union, collection, assembly," verbal noun from gather (v.).
Gatling gun (n.): 1864, named for its designer, U.S. inventor Richard Jordan Gatling (1818-1903); patented by 1862 but not used in American Civil War until the Petersburg campaign of June 1864 as an independent initiative by U.S. Gen. Ben Butler.
For the first time in this war, the Gatling gun was used by Butler in repelling one of Beauregard's midnight attacks. Dispatches state that it was very destructive, and rebel prisoners were very curious to know whether it was loaded all night and fired all day. ["Scientific American," June 18, 1864]
gator (n.): 1844, colloquial shortening of alligator.
GATT: 1947, acronym from General Agreement on Tariffs and Trade.
gau (n.): ancient German territorial and administrative division, originally comprising several villages, surviving in place names such as Breisgau and Oberammergau; also in gauleiter (with leiter "leader"), title of the local political leaders under the Nazi system. Compare the first element in yeoman.
gauche (adj.): "awkward, tactless," 1751 (Chesterfield), from French gauche "left" (15c., replacing senestre in that sense), originally "awkward, awry," from gauchir "turn aside, swerve," from Proto-Germanic *wankjan (source also of Old High German wankon, Old Norse vakka "to stagger, totter"), from PIE *weng- "to bend, curve" (see wink (v.)).
gaucherie (n.): "an awkward action; awkwardness," 1798, from French gaucherie, from gauche (see gauche).
gaucho (n.): "a Spanish-descended native of the pampas," 1824, guacho, from Spanish gaucho, probably from a native South American language. Compare Araucanian (native language spoken in part of Chile) cauchu "wanderer." Noted for their independence and skill in horsemanship and with the lasso.
gaud (n.): early 15c., "a bauble, trinket," earlier "a large, ornamental bead in a rosary" (mid-14c.), probably mistakenly taken as singular of earlier gaudy (n.) "large, ornamental rosary bead" (early 14c., in plural form gaudeez), later "ornamentation" generally (late 14c.), which is from Medieval Latin gaudia and Old French gaudie "joy, pleasure, playfulness; a piece of showy finery, a flashy trinket," from Latin gaudium "joy," gaude "rejoice thou" (in hymns), from gaudere "rejoice" (see joy (n.), and compare jewel (n.)).

Also in Middle English "a jest, prank, trick" (late 14c.); "a deception, fraud, artifice" (mid-14c.). As a verb, "to furnish with gauds," from late 14c. Related: Gauded; gauding; gaudful; gaudless.
gaudery (n.): "showy decoration," 1590s, from gaud (n.) + -ery.
gaudily (adv.): 1610s, from gaudy + -ly (2).
gaudiness (n.): c. 1600, from gaudy + -ness.
gaudy (adj.): "showy, tastelessly rich," c. 1600; earlier "joyfully festive" (1580s), probably a re-adjectivizing of gaudy (n.) "large, ornamental bead in a rosary" (early 14c.) via the noun gaud + -y (2.). In early Modern English it also could mean "full of trickery" (1520s).

Or possibly the adjective is from or influenced by Middle English noun gaudegrene (early 14c.), name of a yellowish-green color or pigment, originally of dye obtained from the weld plant (see weld (n.1)). This Germanic plant-name became gaude in Old French, and thus the Middle English word. Under this theory, the sense shifted from "weld-dye" to "bright ornamentation."

As a noun, "feast, festival" 1650s, from gaudy day "day of rejoicing" (1560s).