Online Etymology Dictionary

triumvir (n.): "one of three men in the same office or of the same authority," mid-15c., from Latin triumvir, from Old Latin phrase trium virum, genitive plural of tres viri "three men," from tres "three" (see three) + viri, plural of vir "man" (see virile). The Latin plural was triumviri.
triumvirate (n.): 1580s, from Latin triumviratus, from triumvir (see triumvir).
triune (adj.): "three in one," 1630s, from tri- + Latin unus "one" (see one). Related: Triunity.
trivet (n.): three-legged iron stand, 12c., trefet, probably from a noun use of Latin tripedem (nominative tripes) "three-footed," from tri- "three" (see three) + pes "foot," from PIE root *ped- (1) "a foot" (see foot (n.)).
trivia (n.): "trivialities, bits of information of little consequence," by 1932, from the title of a popular book by U.S.-born British aphorist Logan Pearsall Smith (1865-1946) first published in 1902 but popularized in 1918 (with "More Trivia" following in 1921 and a collected edition including both in 1933), containing short essays often tied to observation of small things and commonplace moments. Trivia is Latin, plural of trivium "place where three roads meet;" in transferred use, "an open place, a public place." The adjectival form of this, trivialis, meant "public," hence "common, commonplace" (see trivial). The Romans also had trivius dea, the "goddess of three ways," another name for Hecate, perhaps originally in her triple aspect (Selene/Diana/Proserpine), but also as the especial divinity of crossroads (Virgil has "Nocturnisque hecate triviis ululata per urbes"). John Gay took this arbitrarily as the name of a goddess of streets and roads for his mock Georgic "Trivia: Or, the Art of Walking the Streets of London" (1716); Smith writes in his autobiography that he got the title from Gay.
I KNOW too much; I have stuffed too many of the facts of History and Science into my intellectuals. My eyes have grown dim over books; believing in geological periods, cave dwellers, Chinese Dynasties, and the fixed stars has prematurely aged me. ["Trivia," 1918 edition]
Then noted c. 1965 as an informal fad game among college students wherein one asked questions about useless bits of information from popular culture ("What was Donald Duck's address?") and others vied to answer first.
Nobody really wins in this game which concentrates on sports, comics and television. Everyone knows that Amos's wife on the "Amos 'n' Andy Show" is Ruby, but who knows that she is from Marietta, Georgia? Trivia players do. They also know the fourth man in the infield of Tinker-to-Evers-to-Chance, the Canadian who shot down Baron Von Richtofen, and can name ten Hardy Boy books. ["Princeton Alumni Weekly," Nov. 9, 1965]
The board game Trivial Pursuit was released 1982 and was a craze in U.S. for several years thereafter.
trivial (adj.): "ordinary" (1580s); "insignificant, trifling" (1590s), from Latin trivialis "common, commonplace, vulgar," literally "of or belonging to the crossroads," from trivium "place where three roads meet," in transferred use, "an open place, a public place," from tri- "three" (see three) + via "road" (see via). The sense connection is "public," hence "common, commonplace."

The earliest use of the word in English was early 15c., a separate borrowing in the academic sense "of the trivium" (the first three liberal arts -- grammar, rhetoric, and logic); from Medieval Latin use of trivialis in the sense "of the first three liberal arts," from trivium, neuter of the Latin adjective trivius "of three roads, of the crossroads." Related: Trivially. For sense evolution to "pertaining to useless information," see trivia.
triviality (n.): 1590s, "quality of being trivial," from Middle French trivialite or else from trivial + -ity. Meaning "a trivial thing or affair" is from 1610s. Related: Trivialities.
trivialize (v.): 1836, from trivial + -ize. Related: Trivialized; trivializing.
trivium (n.): 1804, from Medieval Latin trivium (9c.) "grammar, rhetoric, and logic," the first three of the seven liberal arts in the Middle Ages, considered initiatory and foundational to the other four: arithmetic, geometry, astronomy, and music. From Latin trivium, in classical Latin "place where three roads meet; a frequented place; public street, highway" (see trivial).
trochaic (adj.): "composed of trochees," 1580s, from Middle French trochaïque (1540s) or directly from Latin trochaicus, from Greek trokhaikos "pertaining to or consisting of trochees," from trokhaios (see trochee).
trochanter (n.): 1610s as a part of the thigh-bone, from French trochanter (16c.), from Greek trokhanter (Galen), from trekhein "to run" (see truckle (n.)). From 1816 as the second joint of an insect leg.
trochee (n.): metrical foot consisting of a long followed by a short syllable, or an accented followed by an unaccented one, 1580s, from French trochée, from Latin trochaeus "a trochee," from Greek trokhaios (pous), literally "a running (foot)," from trekhein "to run" (see truckle (n.)). Its rapid movement rendered it a fit accompaniment to dances.
trod: past tense of tread (v.).
trodden (adj.): "that has been stepped on," 1540s, past participle adjective from tread (v.). The past participle was altered from Middle English treden under influence of Middle English past participles such as stolen from steal.
trog (n.): "obnoxious person, boor, lout," 1956, short for troglodyte.
troglodyte (n.): "cave-dweller," 1550s, from Middle French troglodyte and directly from Latin troglodytae (plural), from Greek troglodytes "cave-dweller, cave-man" (in reference to tribes identified as living in various places by ancient writers; by Herodotus on the African coast of the Red Sea), literally "one who creeps into holes," from trogle "hole, mouse-hole" (from trogein "to gnaw, nibble, munch;" see trout) + dyein "go in, dive in." Related: Troglodytic.
troika (n.): 1842, "carriage drawn by three horses abreast," from Russian troika "three-horse team, any group of three," from collective numeral troje "group of three" (from PIE *tro-yo-, suffixed form of *trei-, see three) + diminutive suffix -ka. Sense of "any group of three administrators, triumvirate" is first recorded 1945.
Trojan (adj.): Old English Troian "of or pertaining to ancient Troy," from Latin Trojanus, from Troia, Troja "Troy," from the Greek name for the city, said to be from Tros, name of a king of Phrygia, the mythical founder of Troy. Trojan horse was figurative of ambush-from-within in Roman times (equus Troianus); attested in English from 1570s; the computer virus sense is attested by 1982.

As a noun from mid-14c., "inhabitant of ancient Troy;" in early modern English, the noun could mean "a determined fellow, one who fights or works hard," from the Trojans' long resistance to the Greeks in the Trojan War, but also in 17c., it was a colloquial term for "person of dissolute life, carousing companion." The trade name for a brand of prophylactic contraceptive was registered 1927 in U.S.
troll (v.): late 14c., "to go about, stroll," later (early 15c.) "roll from side to side, trundle," probably from Old French troller, a hunting term, "wander, to go in quest of game without purpose" (Modern French trôler), from a Germanic source (compare Old High German trollen "to walk with short steps"), from Proto-Germanic *truzlanan.

Sense of "sing in a full, rolling voice" (first attested 1570s) and that of "fish with a moving line" (c. 1600) both are extended technical uses from the general sense of "roll, trundle," the former from "sing in the manner of a catch or round," the latter perhaps confused with trail or trawl. Figurative sense of "to lure on as with a moving bait, entice, allure" is from 1560s. Meaning "to cruise in search of sexual encounters" is recorded from 1967, originally in homosexual slang.
troll (n.1): supernatural being in Scandinavian mythology and folklore, 1610s (with an isolated use mid-14c.), from Old Norse troll "giant being not of the human race, evil spirit, monster." Some speculate that it originally meant "creature that walks clumsily," and derives from Proto-Germanic *truzlan, from *truzlanan (see troll (v.)). But it seems to have been a general supernatural word, such as Swedish trolla "to charm, bewitch;" Old Norse trolldomr "witchcraft."

The old sagas tell of the troll-bull, a supernatural being in the form of a bull, as well as boar-trolls. There were troll-maidens, troll-wives, and troll-women; the trollman, a magician or wizard, and the troll-drum, used in Lappish magic rites. The word was popularized in literary English by 19c. antiquarians, but it has been current in the Shetlands and Orkneys since Viking times. The first record of the word in modern English is from a court document from the Shetlands, regarding a certain Catherine, who, among other things, was accused of "airt and pairt of witchcraft and sorcerie, in hanting and seeing the Trollis ryse out of the kyrk yeard of Hildiswick."

Originally conceived as a race of malevolent giants, they have suffered the same fate as the Celtic Danann and by 19c. were regarded by peasants in in Denmark and Sweden as dwarfs and imps supposed to live in caves or under the ground.
They are obliging and neighbourly; freely lending and borrowing, and elsewise keeping up a friendly intercourse with mankind. But they have a sad propensity to thieving, not only stealing provisions, but even women and children. [Thomas Keightley, "The Fairy Mythology," London, 1850]
troll (n.2): "act of going round, repetition," 1705, from troll (v.). Meaning "song sung in a round" is from 1820.
trolley (n.): 1823, in Suffolk dialect, "a cart," especially one with wheels flanged for running on a track (1858), probably from troll (v.) in the sense of "to roll." Sense transferred to "device used to transmit electric current to streetcars, consisting of a trolley wheel which makes contact with the overhead wires" (1888), then "streetcar drawing power by a trolley" (1891), which probably is short for trolley-car, attested from 1889.
trollop: 1610s, "slovenly woman," often with implications of moral looseness, probably from troll (v.) in sense of "roll about, wallow."
[A] certain Anne Hayward, wife of Gregory Hayward of Beighton, did in the parishe church of Beighton aforesaid in the time of Divine Service or Sermon there, and when the Minister was reading & praying, violently & boisterously presse & enter into the seat or place where one Elizabeth, wife of Robert Spurlinir, was quietly at her Devotion & Duty to Almighty God and then and there did quarrel chide & braule & being evilly & inalitiously bent did use then and there many rayleing opprobrious Speeches & Invectives against the said Elizabeth calling her Tripe & Trallop, to the great disturbance both of the Minister and Congregation. [Archdeaconry of Sudbury, Suffolk, Court Proceedings, 1682]
trombone (n.): brass wind instrument, 1724, from Italian trombone, augmentative form of tromba "trumpet," from a Germanic source (compare Old High German trumba "trumpet;" see trumpet (n.)).
tromp (v.): 1892, variant of tramp (v.); mainly American English. Related: Tromped; tromping.
trompe l'oeil: 1889, French, literally "deceives the eye," from tromper "to deceive," a verb of uncertain origin and the subject of many theories (see trump (v.2)).
troop (n.): 1540s, "body of soldiers," 1540s, from Middle French troupe, from Old French trope "band of people, company, troop, crowd" (13c.), of uncertain origin, perhaps from Frankish *throp "assembly, gathering of people" or another Germanic source, perhaps related to Old English ðorp, Old Norse thorp "village" (see thorp). OED derives the French word from Latin troppus "flock," which is of unknown origin but also might be from the proposed Germanic source. Of groups of animals from 1580s. Specifically as "a subdivision of a cavalry force" from 1580s; of Boy Scouts from 1908. Troops "armed forces" is from 1590s.
troop (v.): 1560s, "to assemble," from troop (n.). Meaning "to march" is recorded from 1590s; that of "to go in great numbers, to flock" is from c. 1600. Related: Trooped; trooping.
trooper (n.): 1630s, "soldier in a cavalry troop," from troop (n.) + -er (1). Extended to "mounted policeman" (1858, in Australia) then to "state policeman" (U.S.) by 1911.
trope (n.): 1530s, from Latin tropus "a figure of speech," from Greek tropos "a turn, direction, course, way; manner, fashion," in rhetoric, "turn or figure of speech," related to trope "a turning" and trepein "to turn," from PIE root trep- (2) "to turn" (source also of Sanskrit trapate "is ashamed, confused," properly "turns away in shame;" Latin trepit "he turns"). Technically, in rhetoric, "a figure of speech which consists in the use of a word or phrase in a sense other than that which is proper to it" [OED], "as when we call a stupid fellow an ass, or a shrewd man a fox" [Century Dictionary].
trophic (adj.): "of or pertaining to nutrition, food, or nourishment," 1856, from Greek trophikos, from trophe "nourishment, food" (see -trophy).
tropho-: before vowels, troph-, word-forming element meaning "nourishment, food," from comb. form of Greek trophe "nourishment" (see -trophy).
trophy (n.): 1510s, "a spoil or prize of war," from Middle French trophée (15c.) from Latin trophaeum "a sign of victory, monument," originally tropaeum, from Greek tropaion "monument of an enemy's defeat," noun use of neuter of adjective tropaios "of defeat, causing a rout," from trope "a rout," originally "a turning" (of the enemy); see trope. In ancient Greece, spoils or arms taken in battle and set up on the field and dedicated to a god. Figurative extension to any token or memorial of victory is first recorded 1560s. As "a symbolic representation of a classical trophy" from 1630s. Trophy wife attested by 1984.
tropic (n.): late 14c., "either of the two circles in the celestial sphere which describe the northernmost and southernmost points of the ecliptic," from Late Latin tropicus "of or pertaining to the solstice" (as a noun, "one of the tropics"), from Latin tropicus "pertaining to a turn," from Greek tropikos "of or pertaining to a turn or change; of or pertaining to the solstice" (as a noun, "the solstice," short for tropikos kyklos), from trope "a turning" (see trope).

The notion is of the point at which the sun "turns back" after reaching its northernmost or southernmost point in the sky. Extended 1520s to the corresponding latitudes on the earth's surface (23 degrees 28 minutes north and south); meaning "region between the tropics of Cancer and Capricorn" is from 1837.
tropical (adj.): 1520s, "pertaining to the celestial tropics," from tropic + -al (1). In reference to the torrid zones of the earth, from 1690s. Meaning "hot and lush like the climate of the tropics" is first attested 1834.
tropism (n.): 1899, "tendency of an animal or plant to turn or move in response to a stimulus," 1899, abstracted from geotropism or heliotropism, with the second element taken in an absolute sense; ultimately from Greek tropos "a turning" (see trope).
troposphere (n.): 1914, from French troposphère, literally "sphere of change," coined by French meteorologist Philippe Teisserenc de Bort (1855-1913) from Greek tropos "a turn, change" (see trope) + sphaira "sphere" (see sphere). Related: Tropopause.
trot (n.): "a gait faster than a walk and slower than a run," c. 1300, originally of horses, from Old French trot "a trot, trotting" (12c.), from troter "to trot, to go," from Frankish *trotton, from Proto-Germanic *trott- (source also of Old High German trotton "to tread"), derivative of *tred- (see tread (v.)). The trots "diarrhea" is recorded from 1808 (compare the runs).
trot (v.): "go at a quick, steady pace," late 14c., from Old French troter "to trot, to go," from Frankish *trotton (see trot (n.)). Italian trottare, Spanish trotar also are borrowed from Germanic. To trot (something) out originally (1838) was in reference to horses; figurative sense of "produce and display for admiration" is slang first recorded 1845. Related: Trotted; trotting.
troth (n.): "truth, verity," late 12c., from a phonetic variant of Old English treowð "faithfulness, veracity, truth" (see truth). Restricted to Midlands and Northern England dialect after 16c., and to certain archaic phrases (such as plight one's troth). Also see betroth.
Trotskyite (n.): 1919, from Leon Trotsky, assumed name of Russian revolutionary leader Lev Davidovich Bronstein (1879-1940) + -ite (1).
trotter (n.): late 14c. as a type of horse; agent noun from trot (v.). Meaning "foot of a quadruped" is from 1520s. Related: Trotters.
troubadour (n.): 1727, from French troubadour (16c.) "one of a class of lyric poets in southern France, eastern Spain, and northern Italy 11c.-13c.," from Old Provençal trobador, from trobar "to find," earlier "invent a song, compose in verse," perhaps from Vulgar Latin *tropare "compose, sing," especially in the form of tropes, from Latin tropus "a song" (see trope). The alternative theory among French etymologists derives the Old Provençal word from a metathesis of Latin turbare "to disturb," via a sense of "to turn up." Meanwhile, Arabists posit an origin in Arabic taraba "to sing." General sense of "one who composes or sings verses or ballads" first recorded 1826.
trouble (v.): c. 1200, from Old French trubler, metathesis of turbler, torbler "to trouble, disturb; make cloudy, stir up, mix" (11c.), from Vulgar Latin *turbulare, from Late Latin turbidare "to trouble, make turbid," from Latin turbidus (see turbid). Related: Troubled; troubling.
trouble (n.): c. 1200, "agitation of the mind, emotional turmoil," from Old French truble, torble "trouble, disturbance" (12c.), from trubler/torbler (see trouble (v.)). From early 15c. as "a concern, a cause for worry;" 1590s as "something that causes trouble." Meaning "unpleasant relations with the authorities" is from 1550s. Related: Troubles (1510s). Trouble and strife as rhyming slang for "wife" is recorded from 1908.
troubled (adj.): of persons, minds, etc., early 14c.; past participle adjective from trouble (v.). In reference to waters, etc., late 14c.
troublemaker (n.): also trouble-maker, 1843, from trouble (n.) + maker.
troubleshoot (v.): also trouble-shoot, 1918 (implied in troubleshooting), probably a back-formation from troubleshooter.
troubleshooter (n.): also trouble-shooter, 1898, originally one who works on telegraph or telephone lines. From trouble (n.) + agent noun from shoot (v.).
troublesome (n.): 1540s, from trouble (n.) + -some (1). Troublesomeness.