Online Etymology Dictionary

Gail: fem. proper name, in some cases short for Abigail, or from the Hebrew root in that name meaning "rejoicing." Attained its greatest popularity in U.S. as a given name for girls born c.1945-1955.
gaily (adj.): also gayly, late 14c., from Middle English gai (see gay) + -ly (2). "The spelling gaily is the more common, and is supported by the only existing analogy, that of daily" [OED].
gain (n.): late 15c., from Middle French gain, from Old French gaaigne "gain, profit, advantage; booty; arable land" (12c.), from gaaignier "to gain" (see gain (v.)). The original French sense enfolded the notions of "profit from agriculture" and "booty, prey." Implied earlier in Middle English gaignage (late 14c.) "profit from agriculture."
gain (v.): 1520s, from Middle French gagner, from Old French gaaignier "to earn, gain; trade; capture, win," also "work in the fields, cultivate land," from Frankish *waidanjan "hunt, forage," also "graze, pasture," from Proto-Germanic *wartho "hunting ground" (cf. Old English waþ "hunting," German Weide "pasture, pasturage," Old Norse veiðr "hunting, catch of fish"), from PIE *weie- "to strive after, pursue with vigor, desire" (see venison). Related: Gained; gaining. To gain on "advance nearer" is from 1719. To gain ground (1620s) was originally military.
gainful (adj.): 1540s (implied in gainfully), from gain + -ful. Phrase gainfully employed attested from 1796.
gainsay (v.): "contradict," c.1300, literally "say against," from Old English gegn- "against" (see again) + say. "Solitary survival of a once common prefix" [Weekley], which was used to form such now-obsolete compounds as gain-taking "taking back again," gainclap "a counterstroke," gainbuy "redeem," and gainstand "to oppose." Related: Gainsaid; gainsaying.
gainst: shortened form of against.
gait (n.): c.1300, gate "a going or walking, departure, journey," earlier "way, road, path" (c.1200), from a Scandinavian source (cf. Old Norse gata "way, road, path"), cognate with Old High German gazza "street, German Gasse, Gothic gatwo. Meaning "manner of walking" is from mid-15c. Modern spelling developed before 1750, originally in Scottish. Related: Gaited.
gaiter (n.): "leather cover for the ankle," 1775, perhaps from French guêtre "belonging to peasant attire," from Middle French *guestre, probably from Frankish *wrist "instep," from Proto-Germanic *wirstiz (cf. German Rist "instep;" see wrist). Related: Gaiters.
gal (n.): slang pronunciation of girl, 1795, execrated as a Cockney vulgarism. Gal Friday is 1940, in reference to "Robinson Crusoe."
gala (n.): 1620s, "festive dress or attire," from French en gala, perhaps from Old French gale "merriment," from galer "rejoice, make merry" (see gallant). Klein suggests the French word is from Italian gala (as in phrase vestito di gala "robe of state"), perhaps from Arabic khil'a "fine garment given as a presentation." Sense of "festive occasion" (characterized by display of finery) first recorded 1777.
galactic (adj.): 1839, "of the Milky Way," from Late Latin galacticus, from galaxias (see galaxy). In modern scientific sense "pertaining to (our) galaxy," from 1849.
Galapagos: islands named for the tortoises (Spanish galapagos) who live there; discovered by Europeans in 1535.
Galatians: from Galatia, region in Asia Minor, from Greek Galatia, based on Gaul (see Gaul), in reference to the Gaulish people who conquered the region and settled there 3c. B.C.E.
galavant (v.): variant of gallivant. Related: Galavanted; galavanting.
galaxy (n.): late 14c., from Old French galaxie, from Late Latin galaxias "Milky Way," from Greek galaxias (adj.), in galaxias kyklos, literally "milky circle," from gala (genitive galaktos) "milk" (see lactation). The technical astronomical sense emerged 1848. Figurative sense of "brilliant assembly of persons" is from 1580s. Milky Way is a translation of Latin via lactea.
See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. [Chaucer, "House of Fame"]
Astronomers began to speculate by mid-19c. that some of the spiral nebulae they could see in telescopes were actually immense and immensely distant structures the size and shape of the Milky Way. But the matter was not settled until the 1920s.
Galbraith: surname, from Old Gaelic Gall-Bhreathnach "stranger-Briton," a name given to Britons settled among Gaels.
gale (n.): "storm at sea," 1540s, from gaile "wind," origin uncertain, perhaps from Old Norse gol "breeze," or Old Danish gal "bad, furious" (often used of weather), from Old Norse galinn "bewitched." Or perhaps it is from Old English galan "to sing" (the second element in nightingale), or giellan "to yell." In technical meteorological use, a wind between 32 and 63 miles per hour.
galena (n.): lead ore, lead sulphide, c.1600, from Latin galena "mix of silver and lead; dross from smelting lead," of unknown origin.
Galicia: region in Central Europe, perhaps ultimately from Lithuanian galas "end, peak," in reference to the Carpathian Mountains which rise there, or from the root of Gaul. The region in northwestern Spain of the same name is perhaps from the Celtic root cala "watercourse," or else it, too, might be from Gaul.
Galilee: "northernmost province of Palestine," late 12c., from Latin Galilaea, Greek Galilaia, from Hebrew Haggalil, literally "The District," a compressed form of Gelil haggoyim "the District of Nations" (cf. Isa. viii:23). The adj. Galilean is used both of Christ (1630s), who was born there, and of the Italian astronomer Galileo (1727).
gall (n.1): "bile," Old English galla (Anglian), gealla (W. Saxon) "gall, bile," from Proto-Germanic *gallon- (cf. Old Norse gall, Old Saxon, Old High German galla, German Galle), from PIE root *ghel- "gold, yellow, yellowish-green" (see Chloe). Informal sense of "impudence, boldness" first recorded American English 1882; but meaning "embittered spirit, rancor" is from c.1200, from the medieval theory of humors. Gall bladder recorded from 1670s.
gall (n.2): "sore spot on a horse," Old English gealla "painful swelling," from Latin galla "gall, lump on plant," originally "oak apple," of uncertain origin. Perhaps from or influenced by gall (1) on notion of "poison-sore." German galle, Dutch gal also are from Latin.
gall (v.): "to make sore by chafing," mid-15c., from gall (n.2). Earlier "to have sores, be sore" (early 14c.). Figurative sense of "harass, irritate" is from 1570s. Related: Galled; galling.
Gallagher: surname, from Irish Gallchobhar "foreign-help."
gallant (n.): "man of fashion and pleasure," mid-15c., earlier "dissolute man, rake" (early 15c.); from gallant (adj.).
gallant (adj.): mid-15c., "showy, finely dressed; gay, merry," from Old French galant "courteous," earlier "amusing, entertaining; lively, bold" (14c.), present participle of galer "rejoice, make merry," generally held to be from Latinized verb form of Frankish *wala- "good, well," from Proto-Germanic *wal- (cf. Old High German wallon "to wander, go on a pilgrimage"), from PIE *wel- "to wish, will" (see will (v.)), "but the transition of sense offers difficulties that are not fully cleared up" [OED]. Sense of "politely attentive to women" was adopted 17c. from French.
gallantly (adv.): 1550s, "showily," from gallant + -ly (2). Meaning "with exaggerated courtesy" is from 1610s.
gallantry (n.): 1590s, "fine appearance," from French galanterie (16c.), from Old French galant (see gallant). Meaning "gallant behavior" is from 1630s. Middle English had gallantness "merriment, gaiety, high living" (late 15c.).
galleon (n.): large ship, 1520s, from Old French galion "little ship" (13c.), from Spanish galeón "galleon, armed merchant ship," from Byzantine Greek galea "galley" (see galley) + augmentative suffix -on. In English use, especially of Spanish ships involved in the American trade.
galleria (n.): Italian form of gallery.
gallery (n.): c.1500, from Middle French galerie "a long portico" (14c.), from Medieval Latin galeria, of uncertain origin, perhaps an alteration of galilea "church porch," which is probably from Latin Galilaea "Galilee," the northernmost region of Palestine (see Galilee); church porches sometimes were so called from being at the far end of the church.
Super altare Beatæ Mariæ in occidentali porte ejusdem ecclesiæ quæ Galilæ a vocatur. [c.1186 charter in "Durham Cathedral"]
Sense of "building to house art" first recorded 1590s; that of "people who occupy a (theater) gallery" (contrasted with "gentlemen of the pit") first by Lovelace, 1640s, hence to play to the gallery (1867).
galley (n.): c.1300, from Old French galie, from Medieval Latin galea or Catalan galea, from Late Greek galea, of unknown origin. The word has made its way into most Western European languages. Originally "low, flat-built seagoing vessel of one deck," once common in the Mediterranean; meaning "cooking range on a ship" dates from 1750. The printing sense is from 1650s, from French galée in the same sense, in reference to the shape of the oblong tray that holds the type. As a short form of galley-proof it is attested from 1890.
galleywest: as a destination where you knock something or someone, American English slang, by 1835; considered by OED to be a corruption of western England dialectal collyweston, name of a village in Northamptonshire ("Colin's West Farmstead") that somehow came to signify "askew, not right." But Farmer calls it an Americanism and goes in for it as an "indefinite superlative," and DAS also does not consider the obscure English term to be the source. Early nautical references suggest it might simply be what it looks like: a sailor's generic way of indicating something has been thrown pretty far by impact.
"Matter? why d--n my old shoes, Captain Williams, here is one of that bloody Don Dego's shot gone right through the galley-door, and through the side of the big copper, and knocked all the beef and hot water galley-west. ..." [N.Ames, "Old Sailor's Yarns," New York, 1835]
Gallic (adj.): 1670s, from Latin Gallicus "pertaining to Gaul or the Gauls," from Latin Gallia "Gaul" and Gallus "a Gaul" from a native Celtic name (see Gaelic), though some connect the word with prehistoric West Germanic *walkhoz "foreigners" (see Welsh). Originally used in English rhetorically or mockingly for "French." The cock as a symbol of France is based on the pun of Gallus "a Gaul" and Latin gallus "cock."
It means not simply 'French,' but 'characteristically', 'delightfully', 'distressingly', or 'amusingly' 'French' ... not 'of France', but 'of the typical Frenchman'. [Fowler]
Gallicism (n.): "French word or idiom," 1650s, from Gallic + -ism.
gallimaufry (n.): "a medley," 1550s, from French galimafrée "hash, ragout," from Old French calimafree "sauce made of mustard, ginger, and vinegar; a stew of carp" (14c.), origin unknown, perhaps from Old French galer "to make merry, live well" (see gallant) + Old North French mafrer "to eat much," from Middle Dutch maffelen [Klein]. Weekley sees in the second element the proper name Maufré.
gallinaceous (adj.): "of or resembling domestic fowl," 1783, from Latin gallinaceus, from gallina "hen," from gallus "cock," perhaps a loan-word from a language of Asia Minor.
galling (adj.): "irritating, offensive," 1580s, figurative use of present participle of gall (v.).
gallium (n.): metalic element, discovered by spectral lines in 1875 by French chemist Lecoq de Boisbaudran (1838-1912), who named it apparently in honor of his homeland (see Gallic), but it has been suggested that he also punned on his own name (cf. Latin gallus "cock").
gallivant (v.): 1809, probably a playful elaboration of gallant in an obsolete verbal sense of "play the gallant, flirt, gad about." Related: Gallivanted; gallivanting.
Young Lobski said to his ugly wife,
"I'm off till to-morrow to fish, my life;"
Says Mrs. Lobski, "I'm sure you a'nt",
But you brute you are going to gallivant."

What Mrs. Lobski said was right,
Gay Mr. Lobski was out all night.
He ne'er went to fish, 'tis known very well
But where he went I shall not tell.

["Songs from the Exile," in "Literary Panorama," London, 1809]
Gallo-Romance: "belonging to Gaul when it was part of the Roman Empire," especially of its language, 1841, from comb. form of Gaul + Romance in the linguistic sense.
gallon (n.): liquid measure, late 13c., from Old North French galon, corresponding to Old French jalon "liquid measure," related to jale "bowl," from Medieval Latin diminutive form galleta "bucket, pail," also "a measure of wine," of unknown origin, perhaps from Gaulish galla "vessel."
gallop (v.): early 15c., from Middle French galoper (12c.), cognate of Old North French waloper, from Frankish *wala hlaupan "to run well" (see wallop). Related: Galloped; galloping.
gallop (n.): 1520s, from gallop (v.).
gallow: singular of gallows.
Galloway: district in southwestern Scotland, Medieval Latin Gallovidia, from Welsh Gallwyddel, Irish Gallgaidhil, literally "foreign Gaels." The adjective Galwegian is on analogy of Norwegian.
gallows (n.): c.1300, plural of Middle English galwe "gallows" (mid-13c.), from Old Norse galgi "gallows," or from Old English galga (Mercian), gealga (West Saxon) "gallows;" all from Proto-Germanic *galgon- "pole" (cf. Old Frisian galga, Middle High German galge "gallows, cross," German Galgen "gallows," Gothic galga "cross"), from PIE *ghalgh- "branch, rod" (cf. Lithuanian zalga "pole, perch," Armenian dzalk "pole"). In Old English, also used of the cross of the crucifixion. Plural because made of two poles.
gallstone (n.): 1758, from gall (n.1) + stone (n.).
Gallup poll: 1940, from George H. Gallup (1901-1984), U.S. journalist and statistician, who in 1935 set up the American Institute of Public Opinion.