Online Etymology Dictionary

grundyism (n.): "social censorship of personal conduct in the name of conventional propriety," 1836, from Mrs. Grundy, prudish character in Thomas Morton's 1798 play "Speed the Plow," play and playwright otherwise now forgotten, but the line "What would Mrs. Grundy say?" became proverbial.
grunge (n.): "sloppiness, dirtiness," also "untidy person," 1965, American English teen slang, probably a back-formation from grungy. In reference to the music and fashion style that originated in Seattle is attested from 1989.
grungy (adj.): "sloppy, shabby," 1965, American English slang, perhaps based on, or blended from, grubby and dingy.
grunion (n.): type of Pacific fish, 1901, from American Spanish gruñon "grunting fish," from grunir "to grunt," from Latin grunnire, from Greek gryzein "to grunt," from gry "a grunt," imitative. Compare the unrelated American fish called the grunt, "so called from the noise they make when taken."
grunt (v.): Old English grunnettan "to grunt," frequentative of grunian "to grunt," probably imitative (compare Danish grynte, Old High German grunnizon, German grunzen "to grunt," French grogner, Latin grunnire "to grunt"). Related: Grunted; grunting. Grunter "a pig" is from 1640s.
grunt (n.): 1550s, from grunt (v.); as a type of fish, from 1713, so called from the noise they make when hauled from the water; meaning "infantry soldier" emerged in U.S. military slang during Vietnam War (first recorded in print 1969); used since 1900 of various low-level workers. Grunt work first recorded 1977.
gruntle (v.): 1938, in gruntled "pleased, satisfied," a back-formation from disgruntled. The original verb (early 15c.) meant "to utter a little or low grunt," hence "to murmur, complain" (1580s), but was rare or dialectal by 19c.
grutch (v.): c. 1200, grucchen, "to murmur, complain," from Old French grouchier, grocier "to murmur, to grumble," of unknown origin, perhaps from Germanic, probably ultimately imitative. Meaning "to begrudge" is c. 1400. Compare gruccild (early 13c.) "woman who complains," from grutch + suffix of unknown origin. Related: Grutched; grutching. As a noun from c. 1400.
Gruyere: kind of cheese, 1802, from Gruyère, the name of the Swiss town and surrounding district where the cheese is made. The place name is said to be ultimately from Latin grus "crane."
gryphon (n.): alternative or archaic spelling of griffin.
gu-: because g- followed by some vowels in English usually has a "soft" pronunciation, a silent -u- sometimes was inserted between the g- and the vowel in Middle English to signal hardness, especially in words from French; but this was not done with many Scandinavian words where hard "g" precedes a vowel (gear, get, give, etc.). Germanic -w- generally became -gu- in words borrowed into Romance languages, but Old North French preserved the Frankish -w-, and English sometimes borrowed both forms, hence guarantee/warranty, guard/ward, etc.
guacamole (n.): 1920, from American Spanish guacamole, originally Mexican, from Nahuatl (Aztecan) ahuaca-molli, from ahuacatl "avocado" + molli "sauce."
Guadalcanal: largest of the Solomon Islands, discovered 1568 by Spanish explorer Álvaro de Mendaña de Neira and named for his hometown in Spain. The place name contains the Spanish form of Arabic wadi "river" which occurs in other Spanish place names (such as Guadalajara, from Arabic Wadi Al-Bajara "River of the Stones," either a parallel formation to or ultimately a translation of the ancient Iberian name for the river that gave the place its earlier name, based on caruca "stony;" Guadalquivir, from Arabic Al-Wadi Al-Kabir "Big River;" and Guadalupe, from the Arabic river word and the Roman name of the river, Lupus, literally "wolf").
Guam: from Chamorro Guahan, said to mean literally "what we have."
guanine (n.): 1846, from guano, from which the chemical first was isolated, + chemical suffix -ine (2).
guano (n.): c. 1600, from Spanish guano "dung, fertilizing excrement," especially of sea-birds on islands off Peru, from Quechua huanu "dung."
Guarani (n.): South American Indian language, 1797, from a native word.
guarantee (n.): 1670s, "person that gives security," altered (perhaps via Spanish garante or confusion with legalese ending -ee), from earlier garrant "warrant that the title to a property is true" (early 15c.), from Old French garant "defender, protector; warranty; pledge; justifying evidence," from Germanic (see warrant (n.)). For form evolution, see gu-. Sense of the "pledge" itself (which is properly a guaranty) developed 18c.
guarantee (v.): 1791, "to be surety for," from guarantee (n.). Garanten in this sense is from early 15c. Related: Guaranteed; guaranteeing.
guarantor (n.): "one who binds himself that the obligation of another shall be performed," 1811, from guarantee with Latinate agent noun suffix -or substituted for -ee.
guaranty (n.): "act or fact of guaranteeing, a being answerable for the obligations of another," 1590s, garrantye, from earlier garant (see guarantee (n.)) with influence from Old French garantie "protection, defense; safeguard, warranty," originally past participle of garantir "to protect," from the same source. The sense of "pledge given as security" that developed 17c. in guarantee might reasonably have left the sense "act of guaranteeing" to this form of the word, but the forms remain confused.
guard (n.): early 15c., "one who keeps watch, a body of soldiers," also "care, custody, guardianship," and the name of a part of a piece of armor, from Middle French garde "guardian, warden, keeper; watching, keeping, custody," from Old French garder "to keep, maintain, preserve, protect" (see guard (v.)). Abstract or collective sense of "a keeping, a custody" (as in bodyguard) also is from early 15c. Sword-play and fisticuffs sense is from 1590s; hence to be on guard (1640s) or off (one's) guard (1680s). As a football position, from 1889. Guard-rail attested from 1860, originally on railroad tracks and running beside the rail on the outside; the guide-rail running between the rails.
guard (v.): mid-15c., from guard (n.) or from Old French garder "to keep watch over, guard, protect, maintain, preserve" (corresponding to Old North French warder, see gu-), from Frankish *wardon, from Proto-Germanic *wardon "to guard" (see ward (v.)). Italian guardare, Spanish guardar also are from Germanic. Related: Guarded; guarding.
guarded (adj.): 1560, "protected, defended," past participle adjective from guard (v.). Meaning "reserved and cautious in speech, behavior, etc." is from 1728. Related: Guardedly; guardedness.
guardian (n.): "one who guards," early 14c., garden; early 15c., gardein, from Anglo-French gardein (late 13c.), Old French gardien "keeper, custodian," earlier guarden, from Frankish *warding-, from the Germanic source of guard (v.). Specific legal sense is from 1510s. Guardian angel is from 1630s.
guardianship (n.): 1550s, from guardian + -ship.
Guatemala: Central American country, from words in a native language, variously identified as Quauhtemellan "land of the eagle" or Uhatzmalha "mountain where water gushes." Related: Guatemalan.
guava (n.): 1550s, from Spanish guaya, variant of guayaba, from Arawakan (W. Indies) guayabo "guava tree" or Tupi guajava.
gubbertushed (adj.): "Gubber Tushed is when teeth stand out, and not in order." [R. Holme, "Armoury," 1688]. The first element is of obscure origin.
gubernatorial (adj.): 1734, formed in American English from Latin gubernator "a governor" (see govern) + -al (1). OED marks it "Cheifly U.S.," and Century Dictionary says "Chiefly in newspaper use." As English words, gubernator was in use from 1520s, gubernation from mid-15c., but both are rare.
gudgeon (n.1): European small freshwater fish, early 15c., from Middle French goujon, from Old French gojon (14c.), from Latin gobionem (nominative gobio), alteration of gobius, from Greek kobios, a kind of fish, a word of unknown origin. They are easily caught, hence the figurative sense of "a credulous person" (one who will "bite" at "bait"), from 1580s.
gudgeon (n.2): "pivot on the end of a beam," c. 1400, from Old French gojon "pin, peg, spike" (13c.), perhaps somehow an altered sense of gudgeon (n.1).
Guelph (n.): also Guelf, one of the two great parties in medieval Italian politics, characterized by support of the popes against the emperors (opposed to the Ghibellines), 1570s, from Italian Guelfo, from Old High German Welf, name of a princely family that became the ducal house of Brunswick, literally "whelp," originally the name of the founder (Welf I). The family are the ancestors of the present dynasty of Great Britain. The name is said to have been used as a war-cry at the Battle of Weinsberg (1140) by partisans of Henry the Lion, duke of Bavaria, who was of the family, against Emperor Conrad III; hence it was adopted in Italy as the name of the anti-imperial party in the Middle Ages.
guerdon (n.): "reward, recompense" (now only poetic), late 14c., from Old French guerdon, guerredon "reward, recompense, payment," from Medieval Latin widerdonum, from Old High German widarlon "recompense," from widar "against," from Proto-Germanic *withro- (see with) + lon "reward," from Proto-Germanic *launam, from PIE *lau- "gain, profit" (see lucre). Compare Old English wiðerlean "requital, compensation." Form influenced in Medieval Latin by Latin donum "gift." Compare Spanish galardon, Italian guiderone.
guerilla (n.): common misspelling (now perhaps established as a variant) of guerrilla (q.v.); compare French guérilla.
Guernsey: Channel Island, the name is Viking. The second element of the name is Old Norse ey "island;" the first element uncertain, traditionally meaning "green," but perhaps rather representing a Viking personal name, such as Grani. Like neighboring Jersey, it was also taken as the name for a coarse, close-fitting vest of wool (1839), worn originally by seamen, and in Australia the word supplies many of the usages of jersey in U.S. As a type of cattle bred there, from 1784.
guerrilla (n.): "fighter in an irregular, independent armed force," 1809, from Spanish guerrilla "body of skirmishers, skirmishing warfare," literally "little war," diminutive of guerra "war," from a Germanic source cognate with Old High German werra "strife, conflict, war," from Proto-Germanic *werra- (see war (n.)). Acquired by English during the Peninsular War (1808-1814), when bands of Spanish peasants and shepherds annoyed the occupying French. Purists failed in their attempt to keep this word restricted to "irregular warfare" and prevent it taking on the sense properly belonging to guerrillero "guerrilla fighter." Figurative use by 1861. As an adjective from 1811.
guess (v.): c. 1300, gessen "to infer from observation, perceive, find out; form an opinion, judge, decide, discern; evaluate, estimate the number, importance, etc. of," perhaps from Scandinavian (compare Middle Danish gitse, getze "to guess," Old Norse geta "guess, get"), or from or influenced by Middle Dutch gessen, Middle Low German gissen "to guess," all from Proto-Germanic *getan "to get" (see get (v.)). The prehistoric sense evolution then would be from "get," to "take aim at," to "to estimate." Meaning "to hit upon the right answer" is from 1540s. Spelling with gu- is late 16c., sometimes attributed to Caxton and his early experience as a printer in Bruges. Related: Guessed; guessing. Guessing game attested from 1650s. To keep (someone) guessing "keep him in a state of suspense" is from 1896, American English.
[T]he legitimate, English sense of this word is to conjecture; but with us, and especially in New England, it is constantly used in common conversation instead of to believe, to suppose, to think, to imagine, to fancy. [Bartlett, "Dictionary of Americanisms," 1848]
guess (n.): c. 1300, "indiscriminate conclusion, guesswork, doubtful supposition," from guess (v.). Mid-15c. as "considered opinion." Verbal shrug phrase your guess is as good as mine attested from 1902.
guess-work (n.): also guesswork, "what is done by or due to guess," 1725, from guess (v.) + work (n.).
guesstimate (v.): 1902, a blending of guess (v.) and estimate (v.). Related: Guesstimated; guesstimating. As a noun from 1906.
guest (n.): Old English gæst, giest (Anglian gest) "an accidental guest, a chance comer, a stranger," from Proto-Germanic *gastiz (source also of Old Frisian jest, Dutch gast, German Gast, Gothic gasts "guest," originally "stranger"), from PIE root *ghos-ti- "stranger, guest; host" (source also of Latin hostis, in earlier use "a stranger," in classical use "an enemy," hospes "host," from *hosti-potis "host, guest," originally "lord of strangers;" Greek xenos "guest, host, stranger;" Old Church Slavonic gosti "guest, friend," gospodi "lord, master"); the root sense, according to Watkins, probably is "someone with whom one has reciprocal duties of hospitality," representing "a mutual exchange relationship highly important to ancient Indo-European society." But as strangers are potential enemies as well as guests, the word has a forked path.

Spelling evolution influenced by Old Norse cognate gestr (the usual sound changes from the Old English word would have yielded Modern English *yest). Meaning "person entertained for pay" (at an inn, etc.) is from late 13c. Old English also had cuma "stranger, guest," literally "a comer." Phrase be my guest in the sense of "go right ahead" first recorded 1955.
guest (v.): early 14c., "receive as a guest;" 1610s, "be a guest;" 1936, American English, "appear as a guest performer," from guest (n.). Related: Guested; guesting.
guest star (n.): 1914 in the entertainment sense; earlier the phrase was used literally, of novae. As a verb, by 1942.
guest-room (n.): also guestroom, 1630s, from guest (n.) + room (n.). Guest chamber is recorded from 1520s. Old English had giestærn "guest-chamber," with the second element the same one as in barn.
guff (n.): "empty talk, nonsense," 1888, from earlier sense of "puff of air" (1825), of imitative origin.
guffaw (n.): 1720, Scottish, probably imitative of the sound of coarse laughter. Compare gawf (early 16c.) "loud, noisy laugh." The verb is from 1721. Related: Guffawed; guffawing.
Guggenheim (n.): grant for advanced study, from the John Simon Guggenheim Foundation, established 1925 by U.S. Sen. Simon Guggenheim (1867-1941) in memory of his son, who died young. The senator's brother was an arts patron who founded the Solomon R. Guggenheim Foundation in 1937, which grew into the Guggenheim Museum of modern art. The surname is German, said to mean literally "swamp hamlet" or "cuckoo hamlet."
guidance (n.): 1530s, "the process of directing conduct," hybrid from guide (v.) + -ance; replacing 15c. guying. In reference to direction in school, career, marriage, etc., from 1927.
guide (v.): late 14c., "to lead, direct, conduct," from Old French guider "to guide, lead, conduct" (14c.), earlier guier, from Frankish *witan "show the way" or a similar Germanic source, from Proto-Germanic *witanan "to look after, guard, ascribe to, reproach" (source also of German weisen "to show, point out," Old English witan "to reproach," wite "fine, penalty"), from PIE *weid- "to see" (see vision). The form of the French word influenced by Old Provençal guidar (n.) "guide, leader," or Italian guidare, both from the same source. Related: Guided; guiding. Guided missile, one capable of altering course in flight, is from 1945.