Online Etymology Dictionary

gainly (adj.): "well-formed and agile," 1886, probably a back-formation from ungainly. Earlier "ready, prompt" (1620s), from gain (n.).
gainsay (v.): "contradict, deny, dispute," c. 1300, literally "say against," from gain- (Old English gegn- "against;" see again) + say (v.). In Middle English it translates Latin contradicere. "Solitary survival of a once common prefix" [Weekley]. It also figured in such now-obsolete compounds as gain-taking "taking back again," gainclap "a counterstroke," gainbuy "redeem," Gaincoming "Second Advent," and gainstand "to oppose." Related: Gainsaid; gainsaying.
gainst (adv.): also '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 (compare Old Norse gata "way, road, path"), from Proto-Germanic *gatwon "a going" (source also of Old High German gazza "street," German Gasse "a way, road," Gothic gatwo), perhaps from PIE *ghe- "to release, let go." Meaning "manner of walking, carriage of the body while walking" is from mid-15c. Modern spelling developed before 1750, originally in Scottish. Related: Gaited.
gaiter (n.): "leather cover for the ankle," 1775, from French guêtre "belonging to peasant attire," of unknown origin; perhaps from Middle French *guestre, from Frankish *wrist "instep," from Proto-Germanic *wirstiz (source also of German Rist "instep;" see wrist (n.)). Related: Gaiters; gaitered (1760).
gal (n.): slang pronunciation of girl, 1795, originally noted as a vulgarism (in Benjamin Dearborn's "Columbian Grammar"). Compare gell, 19c. literary form of the Northern England dialectal variant of girl, also g'hal, the girlfriend of a b'hoy (1849). Gal Friday is 1940, in reference to "Robinson Crusoe."
gala (n.): 1620s, "festive dress or attire" (obsolete), 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. Quasi-adjectival use in gala day "day of festivities," etc.
galactic (adj.): 1839, "of the Milky Way, of the bright band of stars around the night sky," from Late Latin galacticus, from galaxias (see galaxy). In modern scientific sense "pertaining to (our) galaxy," from 1849. From 1844 as "of or pertaining to milk."
galacto-: before vowels galact-, word-forming element meaning "milk, milky," from Greek gala (stem galakt-; see galaxy).
Galapagos: islands were named for the tortoises (Spanish galapagos) who live there; discovered by Europeans in 1535. Related: Galapagian.
Galatians (n.): Biblical epistle, from Galatia, name of an ancient inland region in Asia Minor, from Greek Galatia, based on Gaul, in reference to the Gaulish people who conquered the region and settled there 3c. B.C.E. In Latin Gallograeci, hence Middle English Gallocrecs "the Gallatians."
galavant (v.): variant of gallivant. Related: Galavanted; galavanting.
galaxy (n.): late 14c., from French galaxie or directly from Late Latin galaxias "the Milky Way" as a feature in the night sky (in classical Latin via lactea or circulus lacteus)from Greek galaxias (adj.), in galaxias kyklos, literally "milky circle," from gala (genitive galaktos) "milk" (see lacto-). The technical astronomical sense in reference to the discrete stellar aggregate including the sun and all visible stars emerged by 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"]
Originally ours was the only one known. 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 in the affirmative until the 1920s.
Galbraith: surname, from Old Gaelic Gall-Bhreathnach "stranger-Briton," a name given to Britons settled among Gaels. Compare Galloway.
gale (n.): "strong wind," especially at sea, 1540s, from gaile "wind," origin uncertain. Perhaps from Old Norse gol "breeze," or Old Danish gal "bad, furious" (often used of weather), which are related to Old Norse galinn "furious, mad, frantic; enchanted, bewitched," from gala "to sing, chant," the wind so called from its raging or on the notion of being raised by spells (but OED finds reason to doubt this). Or perhaps it is named for the sound, from Old English galan "to sing," or giellan "to yell." The Old Norse and Old English words all are from the source of yell (v.). In nautical use, between a stiff breeze and a storm; in technical meteorological use, a wind between 32 and 63 miles per hour.
Galen: celebrated Greek physician of 2c.; his work still was a foundation of medicine in the Middle Ages and his name is used figuratively for doctors.
galena (n.): lead ore, lead sulphide, c. 1600, from Latin galena "mix of silver and lead; dross from smelting lead," of unknown origin. Related: Galenic.
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 from the ancient Roman province of Gallaecia, which is perhaps from the Celtic root cala "watercourse," or else it, too, might be from the root of Gaul. Related: Galician (1749 of Spain, 1835 of Eastern Europe).
Galilee: "northernmost province of Palestine," late 12c., from Latin Galilaea, Greek Galilaia, with place-name element + Hebrew Haggalil, literally "The District," a compressed form of Gelil haggoyim "the District of Nations" (see Isa. viii:23). The adjective Galilean, also Galilaean, is used both of Jesus, who was raised and began preaching there, and his followers (1610s), who was born there, and of the Italian astronomer Galileo Galilei (1727); the family name is from one of its ancestors, Galileo de'Bonajuti, a prominent 15th century physician and civic leader in Florence, and represents Latin Galilaeus "Galilean." Galilean also figures as the word applied to early Christians among the pagans and Jews. Old and Middle English had Galileish
gall (n.1): "bile, liver secretion," Old English galla (Anglian), gealla (West Saxon) "gall, bile," from Proto-Germanic *gallon "bile" (source also of Old Norse gall "gall, bile; sour drink," Old Saxon galle, Old High German galla, German Galle), from PIE root *ghel- (2) "to shine," with derivatives referring to bright materials and gold, and bile or gall (see glass). 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 (n.2): "sore on skin caused by rubbing or chafing," Old English gealla "painful swelling, sore spot on a horse," probably from Latin galla "gall, lump on plant," originally "oak-gall" (see gall (n.3)). Perhaps from or influenced by gall (n.1) on notion of "poison-sore." Meaning "bare spot in a field" (1570s) is probably the same word. German galle, Dutch gal also are said to be 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, vex, irritate, chafe the spirit of," is from 1570s. A past-participle adjective gealled is found in Old English, but OED says this is from the noun. Related: Galled; galling.
gall (n.3): "excrescence on a plant caused by the deposit of insect eggs," especially on an oak leaf, late 14c., from Latin galla "oak-gall," which is of uncertain origin. They were harvested for use in medicines, inks, dyes.
gall-bladder (n.): 1670s, from gall (n.1) + bladder.
Gallagher: surname, from Irish Gallchobhar "foreign-help." Compare Galloway.
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," which is of uncertain origin. Perhaps from a Latinized verb formed from Frankish *wala- "good, well," from Proto-Germanic *wal- (source also of Old High German wallon "to wander, go on a pilgrimage"), from PIE root *wel- (2) "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 early 17c. from French. Attempts to distinguish this sense by accent are an 18c. artifice.
gallant (n.): mid-15c., "man of fashion and pleasure," earlier "dissolute man, rake" (early 15c.); from gallant (adj.). As "one who is particularly attentive to women" probably by late 15c.
gallantly (adv.): 1550s, "showily," from gallant (adj.) + -ly (2). Meaning "with exaggerated courtesy toward women" is from 1610s.
gallantry (n.): 1590s, "fine appearance," from French galanterie (16c.), from Old French galant "courteous; amusing" (see gallant (adj.)). Meaning "gallant behavior" is from 1630s; meaning "polite attention to ladies" is from 1670s. Middle English had gallantness "merriment, gaiety, high living" (late 15c.).
galleon (n.): kind of large ship, 1520s, from French galion "armed ship of burden," and directly from Spanish galeón "galleon, armed merchant ship," augmentative of galea, from Byzantine Greek galea "galley" (see galley) + augmentative suffix -on. Developed 15c.-16c., it was shorter, broader, and with a higher stern superstructure than the galley. In English use, especially of Spanish royal treasure-ships or the government warships that escorted private merchant ships in the South American trade.
GALLEON. The accepted term for the type of ship which the Spaniards used in 1588; that is, an armed merchantman of exceptional quality, combining the strength of the mediaeval trader with some of the finer lines and fighting features of the GALLEY. [Sir Geoffrey Callender, "Sea Passages," 1943]
Italian agumented form of galea, galeaza, led to a different 16c. ship-name in English, galliass (1540s).
galleria (n.): Italian form of gallery.
gallery (n.): mid-15c., "covered walk or passageway, narrow and partly open passageway along a wall," from Old French galerie "a long portico" (14c.), from Medieval Latin galeria, of unknown 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, perhaps 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. In reference to theaters, of the section with the highest, cheapest seats; hence "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.): 13c., "seagoing vessel having both sails and oars," from Old French galie, galee "boat, warship, galley," 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 a common type in the Mediterranean. Meaning "cooking range or cooking room on a ship" dates from 1750.

The printing sense of galley, "oblong tray that holds the type once set," is from 1650s, from French galée in the same sense, in reference to the shape of the tray. As a short form of galley-proof it is attested from 1890.
galley-slave (n.): 1560s, from galley (n.) in the "ship" sense + slave (n.). The ships were often rowed by slaves or convicts.
galleywest (adv.): indicating where something or someone is knocked, "into an extremely distressed or disabled condition," 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, based on galley in the "ship's cooking room" sense.
"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, "of or pertaining to the French," 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" (see gallinaceous). Earlier was Gallican (1590s).
It means not simply 'French,' but 'characteristically', 'delightfully', 'distressingly', or 'amusingly' 'French' ... not 'of France', but 'of the typical Frenchman'. [Fowler]
As "of or pertaining to the ancient Gauls" from 1796.
Gallicism (n.): "French word or idiom," 1650s, from Gallic + -ism.
gallimaufry (n.): "a medley, hash, hodge-podge," 1550s, from French galimafrée "hash, ragout, dish made of odds and ends," from Old French galimafree, calimafree "sauce made of mustard, ginger, and vinegar; a stew of carp" (14c.), which is of unknown origin. 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. Hence, figuratively, "any inconsistent or absurd medley."
gallinaceous (adj.): "of or resembling domestic fowl," 1783, from Latin gallinaceus "of hens, of fowls, pertaining to poultry," from gallina "hen," a fem. formation from gallus "cock," probably from PIE root *gal- (2) "to call, shout" (see call (v.)) as "the calling bird." But it also has an ancient association with Gaul (see Gallic), and some speculate that this is the source of the word, "on the assumption that the Romans became acquainted with the cock from Gaul, where it was brought by the Phoenicians" [Buck].
galling (adj.): "irritating, offensive, extremely annoying," 1580s, figurative use of present participle of gall (v.).
gallinicide (n.): "the killing of chickens," 1883, from Latin gallina "hen" (see gallinaceous) + -cide.
gallinivorous (adj.): "chicken-eating," 1862, from Latin gallina "hen" (see gallinaceous) + -vorous.
galliot (n.): "small galley," mid-14c., from Old French galiote, galiot "small ship," diminutive of galie (see galley).
gallipot (n.): "small glazed pot," mid-15c., of uncertain origin; perhaps from French, perhaps literally "galley pot," meaning one imported from the Mediterranean on galleys.
gallium (n.): metalic element that melts in the hand, 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 (compare Latin gallus "cock," for which see gallinaceous). With metallic element ending -ium.
gallivant (v.): "gad about, spend time in frivolous pleasure-seeking, especially with the opposite sex," 1809, of uncertain origin, perhaps 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-Roman (adj.): "belonging to Gaul when it was part of the Roman Empire," from comb. form of Gaul + Roman. In reference to a language, and as a noun, the language spoken in France from the end of the fifth century C.E. to the middle of the ninth, a form of Vulgar Latin with local modifications and additions from Gaulish that then, in the region around Paris, developed into what linguists call Old French.
Gallomania (n.): 1797, from comb. form of Gaul + -mania. Jefferson used adjective Gallomane (1787).
gallon (n.): English measure of capacity (containing four quarts), usually for liquids, late 13c., from Old North French galon, corresponding to Old French jalon, name of a liquid measure roughly equivalent to a modern gallon," which is related to (perhaps augmentative of) jale "bowl," from Medieval Latin or Vulgar Latin diminutive form galleta "bucket, pail," also "a measure of wine," a word of unknown origin, perhaps from Gaulish galla "vessel."
gallop (v.): "move or run by leaps," early 15c., from Old French galoper "to gallop" (12c.), central Old French form of Old North French waloper, probably from Frankish *wala hlaupan "to run well" (see wallop). Related: Galloped; galloping. Though the French word is Germanic, Dutch galopperen, German galoppiren, Swedish galoppera are from French.