Online Etymology Dictionary

trichotillomania (n.): 1905, from French trichotillomanie (1889), from tricho-, Latinized form of Greek trikho-, comb. form of thrix (genitive trikhos) "hair" + Greek tillesthai "to pull out" + mania.
trick (n.): early 15c., "a cheat, a mean ruse," from Old North French trique "trick, deceit, treachery, cheating," from trikier "to deceive, to cheat," variant of Old French trichier, probably from Vulgar Latin *triccare, from Latin tricari "be evasive, shuffle," from tricæ "trifles, nonsense, a tangle of difficulties," of unknown origin.

Meaning "a roguish prank" is recorded from 1580s; sense of "the art of doing something" is first attested 1610s. Meaning "prostitute's client" is first attested 1915; earlier it was U.S. slang for "a robbery" (1865). Trick-or-treat is recorded from 1942.
trick (v.): 1590s, from trick (v.). Related: Tricked; tricking. An earlier sense of "to dress, adorn" (c.1500) is perhaps a different word entirely.
trickery (n.): 1800, from trick (v.) + -ery.
trickle (n.): 1570s, from trickle (v.).
trickle (v.): late 14c., possibly a shortened variant of stricklen "to trickle," a frequentative form of striken "to flow, move" (see strike). Related: Trickled; trickling. Trickle-down as an adjectival phrase in an economic sense first recorded 1944; the image had been in use at least since Teddy Roosevelt.
trickster (n.): 1711, from trick (n.) + -ster.
tricky (adj.): 1786, "characterized by tricks," from trick (n.) + -y (2). Meaning "deceptively difficult" is from 1868. Related: Trickily; trickiness. Earlier was tricksy (1590s).
tricolor (n.): 1798, "flag having three colors," especially the emblem of France adopted during the Revolution, from French tricolore, in drapeau tricolore "three-colored flag." The arrangement of colors on the modern French national flag dates from 1794.
tricot (n.): 1859, from French tricot "knitting, knitted work," from tricoter "to knit," probably a variant of Old French estriquer "to smooth," from a Germanic source (e.g. Middle Low German striken "pass over lightly").
tricuspid (n.): 1660s, from Latin tricuspidem (nominative tricuspis) "three-pointed," from tri- (see tri-) + cuspis "point" (see cusp).
tricycle (n.): 1828, "three-wheeled horse-drawn carriage," from French tricycle (1827); see tri- + cycle (n.). The pedal-powered version is first attested 1868.
trident (n.): mid-15c., from Latin tridentem (nominative tridens; genitive tridentis) "three-pronged, three-toothed," from tri- "three" + dens (genitive dentis) "tooth" (see tooth). As a type of U.S. nuclear-powered submarine, recorded from 1972.
triennial (adj.): 1630s, "lasting three years;" 1640s, "occurring every three years," from Latin triennium "three-year period," from tri- "three" + annus "year" (see annual). For vowel change, see biennial.
Trier: city in Germany (French Trèves), founded c.15 B.C.E. by Augustus, named for the indigenous Gaulish people, the Treveri.
trifecta (n.): 1974, from tri- + perfecta.
trifid (adj.): "divided into three lobes," 1620s, from Latin trifidus "cleft in three," from tri- "three" + -fid. This adjective probably inspired triffid, the name of the three-legged walking poisonous plants in John Wyndham's novel "The Day of the Triffids" (1951).
trifle (n.): early 13c., trufle "false or idle tale," later "matter of little importance" (late 13c.), from Old French trufle "mockery," diminutive of truffe "deception," of uncertain origin.
trifle (v.): "treat lightly," 1520s, from trifle (n.). Related: Trifled; trifling.
trig (adj.): "smart, trim," c.1200, from Old Norse tryggr "firm, trusty, true" (see true (adj.)). A Scottish and northern word only until 19c.
trigeminal (adj.): 1830, from Latin trigeminus "born in threes;" see tri- + geminate.
trigger (n.): 1650s, earlier tricker (1620s), from Dutch trekker "trigger," from trekken "to pull" (see trek). Tricker was the usual form in English until c.1750. Trigger-happy is attested from 1943.
trigger (v.): 1930, from trigger (n.). Related: Triggered; triggering.
triglyceride (n.): 1860, malformed from tri- + glyceride. So called for the three radicals.
trigonometry (n.): "branch of mathematics that deals with relations between sides and angles of triangles," 1610s, from Modern Latin trigonometria (Barthelemi Pitiscus, 1595), from Greek trigonon "triangle" (from tri- "three" + gonia "angle;" see knee) + metron "a measure" (see meter (n.2)).
trike (n.): short for tricycle, 1883.
trilateral (adj.): 1650s, from Latin trilaterus "three-sided;" see tri- + lateral. The Trilateral Commission (representing Japan, the U.S., and Europe) was founded 1973.
trilby (n.): type of hat, 1897, from name of Trilby O'Ferrall, eponymous heroine of the novel by George du Maurier (1834-1896), published in 1894. In the stage version of the novel, the character wore this type of soft felt hat. In plural, also slang for "feet" (1895), in reference to the eroticism attached to the heroine's bare feet.
trilingual (adj.): 1834, from tri- + Latin lingua "language," literally "tongue" (see lingual).
trill (n.): 1640s, from Italian trillio, triglio "a quavering or warbling in singing," probably of imitative origin. The verb is 1660s, from Italian trillare "to quaver, trill." Related: Trilled; trilling.
trillion: 1680s, from French trillion (late 15c.), from tri- + (m)illion. Cf. billion. In the U.S., the fourth power of a thousand (one thousand billion, 1 followed by 12 zeroes); in Great Britain, the third power of a million (one million billion, 1 followed by 18 zeroes), which is the original sense.
trillium (n.): 1768, from Modern Latin trillium (Linnaeus, 1753), from Latin tri- "three" (see three). So called for its leaves.
trilobite (n.): extinct marine arthropod, 1832, from Modern Latin Trilobites (Walch, 1771), from Greek tri- "three" (see three) + lobos "lobe" (see lobe); so called because its body is divided into three lobes.
trilogy (n.): "any series of three related works," 1660s, from Greek trilogia "series of three related tragedies performed at Athens at the festival of Dionysus," from tri- "three" (see three) + logos "story" (see logos).
trim (v.): probably from Old English trymman "strengthen, make ready," from trum "strong, stable," from Proto-Germanic *trumaz; said to be cognate with Sanskrit drumah "tree," Greek drymos "copse, thicket," drys "tree, oak," and Old English treow (see tree). Examples in Middle English are wanting.

Original sense is preserved in nautical phrase in fighting trim (see trim (n.)). Meaning "make neat by cutting" is first recorded 1520s; that of "decorate, adorn" is from 1540s. Sense of "reduce" is attested from 1966. The adjective sense of "in good condition, neat, fit" is attested from c.1500, probably ultimately from Old English adjective trum.
trim (n.): "state of being prepared," 1580s, nautical jargon, from trim (v.). The meaning "visible woodwork of a house" is recorded from 1884; sense of "ornamental additions to an automobile" is from 1922. Slang meaning "a woman regarded as a sex object" is attested from 1955, American English.
trimester (n.): 1821, "period of three months," from French trimestre (early 17c.), from Latin trimestris "of three months," from tri- "three" + mensis "month" (see moon (n.)). Specific obstetrics sense is attested from 1916.
trimeter (n.): "a verse of three metrical feet," 1560s, from Latin trimetrus, from Greek trimetros "having three measures," from tri- "three" + metron "a measure" (see meter (n.2)).
trimmer (n.): "one who changes opinions, actions, etc. to suit circumstances," 1680s, agent noun from trim (v.) in a nautical sense of "distribute the load of a ship so she floats on an even keel" (1570s), hence, "to adjust the balance of sails or yards with reference to the wind's direction" (1620s).
trimmings (n.): "adornments, accessories, etc.," 1610s, from trim (v.).
trine (adj.): "threefold," late 14c., from French trine (13c.), from Latin trinus "threefold," from tres "three" (see three).
trinity (n.): early 13c., "the Father, Son and Holy Spirit," constituting one God in prevailing Christian doctrine, from Old French trinite (11c.), from Latin trinitatem (nominative trinitas) "Trinity, triad" (Tertullian), from trinus "threefold, triple," from plural of trini "three at a time, threefold," related to tres (neuter tria) "three." The Latin word was widely borrowed in European languages with the rise of Christianity (e.g. Irish trionnoid, Welsh trindod, German trinität).
trinket (n.): 1530s, of unknown origin. Evidently a diminutive form, perhaps related to trick.
trinomial: 1670s, from tri- + second element from binomial.
trio (n.): 1724, from French trio (c.1600), from Italian trio, from tri- "three" (see three); patterned on duo.
trip (v.): late 14c. (implied in tripper), "tread or step lightly, skip, caper," from Old French tripper "strike with the feet" (12c.), from a Germanic source (cf. Middle Dutch trippen "to skip, trip, hop," Low German trippeln, Frisian tripje, Dutch trappen, Old English treppan "to tread, trample") related to trap.

The sense of "strike with the foot and cause to stumble" is first recorded early 15c. Meaning "to release" (a catch, lever, etc.) is recorded from 1897; trip-wire is attested from 1916. Related: Tripped; tripping.
trip (n.): "act or action of tripping," 1650s, from trip (v.); sense of "a short journey or voyage" is from 1690s, originally a nautical term, the connection is uncertain. The meaning "psychedelic drug experience" is first recorded 1959 as a noun; the verb in this sense is from 1966, from the noun.
tripartite (adj.): early 15c., "divided in three," from Latin tripartitus "divided into three parts," from tri- "three" (see three) + partitus, past participle of partiri "to divide" (see part (v.)).
tripe (n.): c.1300, from Old French tripe "entrails used as food" (13c.), of unknown origin, perhaps via Spanish tripa from Arabic therb "suet" (but also said to mean "fold of a piece of cloth"). Applied contemptuously to persons (1590s), then to anything considered worthless, foolish, or offensive (1892).
triple (v.): late 14c., from Medieval Latin triplare "to triple," from Latin triplus "threefold, triple," from tri- "three" + -plus "-fold." The noun is recorded from early 15c.; the baseball sense is attested from 1880. The adjective is recorded from 1540s.