Online Etymology Dictionary

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," agent noun from troop. Extended to "mounted policeman" (1858, in Australian) then to "state policeman" (U.S.) by 1911.
trope (n.): 1530s, from Latin tropus "a figure of speech," from Greek tropos "turn, direction, turn or figure of speech," related to trope "a turning" and trepein "to turn," from PIE root trep- "to turn" (cf. 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.
trophic (adj.): 1873, from Greek trophikos, from trophe "nourishment" (see -trophy).
tropho-: before vowels, troph-, word-forming element 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," from trope "a rout," originally "a turning" (of the enemy); see trope. Figurative extension to any token or memorial of victory is first recorded 1560s. 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, or to the solstice" (as a noun, "the solstice"), 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 these parallels" is from 1837. Tropical "hot and lush like the climate of the tropics" is first attested 1834.
tropical (adj.): 1520s, "pertaining to the celestial tropics," from tropic + -al (1). In reference to the torrid zones of the earth, from 1690s.
tropism (n.): 1899, "tendency of an animal or plant to turn or move in response to a stimulus," abstracted from geotropism, ultimately from Greek tropos (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).
trot (n.): c.1300, from Old French trot (12c.), from troter "to trot, to go," from Frankish *trotton (cf. Old High German trotton "to tread"), from a variant of the Germanic base of tread (v.). The trots "diarrhea" is recorded from 1808 (cf. the runs).
trot (v.): 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.): late 12c., from a phonetic variant of Old English treowð "faithfulness, truth" (see truth). Restricted to Midlands and Northern England dialect after 16c., and to certain archaic phrases (e.g. plight one's troth). Cf. also 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.
troubadour (n.): 1727, from French troubadour "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.): early 13c., from Old French trubler (11c.), metathesis of turbler, 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, related to trubler (see trouble (v.)). From early 15c. as "a concern, a cause for worry." The Troubles in reference to times of violence and unrest in Ireland is attested from 1880, in reference to the rebellion of 1640s.
troubled (adj.): in reference to waters, etc., late 14c., past participle adjective from trouble (v.).
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 + -some.
trough (n.): Old English trog, from Proto-Germanic *trugoz (cf. Old Frisian, Old Saxon, Old Norse trog, Middle Dutch troch, Dutch trog, Old High German troc, German trog), perhaps ultimately from PIE *drukos, from root *dru- "wood, tree" (see tree). Originally pronounced in English with a hard -gh- (as in Scottish loch); pronunciation shifted to -f-, but spelling remained.
trounce (v.): 1550s, "to trouble, afflict, harass," later "to beat, thrash" (1560s), of uncertain origin. Perhaps related to Middle French troncer "to cut, cut off a piece from," from tronce "piece of timber," from Old French tronc (see trunk). Related: Trounced; trouncing.
troupe (n.): 1825, "company, band," from French troupe, from Middle French troupe "company" (see troop).
trouper (n.): 1890, "actor or performer in a troupe," agent noun from troupe. Transferred sense of "reliable, uncomplaining person" [OED] is attested by 1942, American English.
trousers (n.): 1610s, earlier trouzes (1580s), extended from trouse (1570s), with plural ending typical of things in pairs, from Gaelic or Middle Irish triubhas "close-fitting shorts," of uncertain origin. The unexplained intrusive second -r- is perhaps by influence of drawers.
trousseau (n.): 1817, from French trousseau, originally "a bundle," diminutive of Old French trousse "bundle" (see truss). Italicized as foreign at first, nativized by 1833. The Old French form was borrowed into Middle English early 13c., but it fell from use.
trout (n.): Old English truht "trout," in part from Old French truite, both from Late Latin tructa, perhaps from Greek troktes "a kind of sea fish," literally "nibbler," from trogein "to gnaw," from PIE root *tere- (see throw). In late 17c. slang, trusty trout was used in a sense of "confidential friend."
trove (n.): 1888, from treasure trove (c.1550), from Anglo-French tresor trové (late 12c.), translating Latin thesaurus inventus, literally "treasure found." Originally any precious metal object one finds hidden whose owner is unknown. As this usually meant ancient hoards, the term came to mean "treasure hoard" in popular use. Rendered treasure found from mid-15c.
trow (v.): Old English treowian "to trust, believe," from treow "faith, belief," from Proto-Germanic *truwian (see true). Cognate with German trauen.
trowel (n.): mid-14c., "tool for spreading plaster or mortar," from Old French truele (13c.), from Late Latin truella "small ladle, dipper" (mid-12c.), diminutive of Latin trua "a stirring spoon, ladle, skimmer." The gardening tool was so called since 1796.
troy: late 14c., standard system of weights for gems and precious metals, from Troyes, city in France (ancient Tricasses), former site of a fair at which this weight is said to have been used. Many medieval towns had their own standard weights. The pound troy contains 5,760 grains and is divided into 12 ounces.
truancy (n.): 1784, from truant + -cy.
truant (n.): early 13c., "beggar, vagabond," from Old French truant "beggar, rogue" (12c.), from Gaulish *trougant- (cf. Breton *truan, later truant "vagabond," Welsh truan "wretch," Gaelic truaghan "wretched"). Cf. Spanish truhan "buffoon," from same source. Meaning "one who wanders from an appointed place" is first attested mid-15c. The adjective is recorded from 1540s.
truce (n.): early 13c., triws, variant of trewes, originally plural of trewe "faith, assurance of faith, covenant, treaty," from Old English treow "faith, treaty," from Proto-Germanic *trewwo (cf. Old Frisian triuwe, Middle Dutch trouwe, Dutch trouw, Old High German triuwa, German treue, Gothic triggwa "faith, faithfulness"). Related to Old English treowe "faithful" (see true).

The Germanic word was borrowed into Late Latin as tregua, hence French trève, Italian tregua. Trucial States, the pre-1971 name of the United Arab Emirates, is attested from 1891, in reference to the 1835 maritime truce between Britain and the Arab sheiks of Oman.
truck (n.): "vehicle," 1610s, "small wheel" (especially one on which the carriages of a ship's guns were mounted), probably from Latin trochus "iron hoop," from Greek trokhos "wheel," from trekhein "to run" (see truckle (n.)). Sense extended to "cart for carrying heavy loads" (1774), then in American English to "motor vehicle for carrying heavy loads" (1913), a shortened form of motor truck in this sense (1901).
There have also been lost to the enemy 6,200 guns, 2,550 tanks and 70,000 trucks, which is the American name for lorries, and which, I understand, has been adopted by the combined staffs in North-West Africa in exchange for the use of the word petrol in place of gasolene. [Winston Churchill, address to joint session of U.S. Congress, May 19, 1943]
Truck stop is attested from 1956.
truck (v.1): "to exchange, barter," early 13c., from Old North French troquer "to barter, exchange," from Medieval Latin trocare "barter," of unknown origin. Rare before 1580. Sense of "have dealings with" is first recorded 1610s. The noun is first recorded 1550s, "act or practice of barter." Sense of "vegetables raised for market" is from 1784, preserved in truck farm (1866).
truck (v.2): "to convey on a truck," 1809, from truck (n.). Verbal meaning "dance, move in a cool way," first attested 1935, from popular dance of that name in U.S., supposedly introduced at Cotton Club, 1933.
trucker (n.): 1853, "worker who moves loads using a cart;" agent noun from truck (v.2). The motorized version is by 1935, a shortening of truck driver (1839).
truckle (n.): "small wheel or roller," late 14c., from Anglo-French trocle, from Latin trochlea "a small wheel, sheaf of a pulley," from Greek trokhileia "a pulley," from trokhos "wheel," from trekhein "to run," from PIE root *dhregh- "to run" (cf. Old Irish droch "wheel," Lithuanian pa-drosti "to run fast"). Truckle bed "small bed on wheels that can be stowed under a larger bed" is from mid-15c.
truckle (v.): "give up or submit tamely," 1610s, "sleep in a truckle bed" (see truckle (n.)). Meaning "give precedence, assume a submissive position" (1650s, implied in truckling) is perhaps in reference to that type of bed being used by servants and inferiors, or from it simply occupying the lower position. Related: Truckled; truckling.
truculent (adj.): 1540s, from Latin truculentus "fierce, savage," from trux (genitive trucis) "fierce, wild."
trudge (v.): "to walk laboriously," 1540s, of unknown origin. Related: Trudged; trudging. The noun meaning "an act of trudging" is attested from 1835.
true (adj.): Old English triewe (West Saxon), treowe (Mercian) "faithful, trustworthy," from Proto-Germanic *trewwjaz "having or characterized by good faith" (cf. Old Frisian triuwi, Dutch getrouw, Old High German gatriuwu, German treu, Old Norse tryggr, Gothic triggws "faithful, trusty"), perhaps ultimately from PIE *dru- "tree," on the notion of "steadfast as an oak." Cf., from same root, Lithuanian drutas "firm," Welsh drud, Old Irish dron "strong," Welsh derw "true," Old Irish derb "sure."

Sense of "consistent with fact" first recorded c.1200; that of "real, genuine, not counterfeit" is from late 14c.; that of "agreeing with a certain standard" (as true north) is from c.1550. Of artifacts, "accurately fitted or shaped" it is recorded from late 15c.; the verb in this sense is from 1841. True-love (adj.) is recorded from late 15c.; true-born first attested 1590s. True-false as a type of test question is recorded from 1923.
truffle (n.): "edible fungus," 1590s, from Middle French trufle (late 14c.), from Old French truffe, probably from Old Provençal trufa, metathesized from Late Latin tufera (plural), cognate of Latin tuber "edible root." Another theory notes Italian tartuffo (Milanese tartuffel) "potato," supposedly from terræ tuber. Extended 1926 to powdered, round chocolates that look like truffles.
truism (n.): 1708, from true + -ism; first attested in Swift.
trull (n.): "a low prostitute or concubine; a drab, strumpet, trollop" [OED], 1510s, from German trulle, perhaps cognate with troll (n.), or perhaps from troll (v.), cf. Middle High German trolle "awkward fellow."
truly (adv.): Old English treowlice, from treow (see true).