trifle (v.) Look up trifle at Dictionary.com
"treat lightly," 1520s, from trifle (n.). Earlier "cheat, mock" (c.1300). Related: Trifled; trifling.
trifocals (n.) Look up trifocals at Dictionary.com
1899, from bifocals with tri-.
trig (adj.) Look up trig at Dictionary.com
"smart, trim," c.1200, from Old Norse tryggr "firm, trusty, true," from Proto-Germanic *treuwaz- (see true (adj.)). A Scottish and northern word only until 19c. Related: Trigness.
trig (n.) Look up trig at Dictionary.com
1895 as a shortening of trigonometry.
trigeminal (adj.) Look up trigeminal at Dictionary.com
1815, from Latin trigeminus "born in threes," as a noun, "triplets;" from tri- (see tri-) + geminus "born at the same birth" (see geminate (adj.)).
trigger (n.) Look up trigger at Dictionary.com
"device by means of which a catch or spring is released and a mechanism set in action," 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.) Look up trigger at Dictionary.com
1930, from trigger (n.). Related: Triggered; triggering.
triglyceride (n.) Look up triglyceride at Dictionary.com
1860, malformed from tri- + glyceride. So called for the three radicals which replace the three hydrogen atoms.
trigonometric (adj.) Look up trigonometric at Dictionary.com
1811; see trigonometry + -ic. Related: Trigonometrical (1660s).
trigonometry (n.) Look up trigonometry at Dictionary.com
"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," see tri-, + gonia "angle," see knee (n.)) + metron "a measure" (see meter (n.2)).
trike (n.) Look up trike at Dictionary.com
short for tricycle, 1883.
trilateral (adj.) Look up trilateral at Dictionary.com
1650s, from Late Latin trilaterus "three-sided;" see tri- + lateral. The Trilateral Commission (representing Japan, the U.S., and Europe) was founded 1973. Related: Trilateralism; trilaterally.
trilby (n.) Look up trilby at Dictionary.com
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 in the novel to the heroine's bare feet. Related: Trilbies.
trilemma (n.) Look up trilemma at Dictionary.com
1670s, from dilemma + tri-.
trilingual (adj.) Look up trilingual at Dictionary.com
"involving three languages," 1834, from tri- + Latin lingua "language," literally "tongue" (see lingual). Latin trilinguis meant "triple-tongued," and was used of Cerberus.
trill (n.) Look up trill at Dictionary.com
1640s, from Italian trillio, triglio "a quavering or warbling in singing," probably ultimately of imitative origin. The verb is 1660s, from Italian trillare "to quaver, trill." Related: Trilled; trilling.
trillion Look up trillion at Dictionary.com
1680s, from French trillion, from Italian trilione; see tri- + million. 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. Compare billion.
trillionth Look up trillionth at Dictionary.com
1820, from trillion + -th (1).
trillium (n.) Look up trillium at Dictionary.com
1768, from Modern Latin trillium (Linnaeus, 1753), from Latin tri- "three" (see three). So called for its leaves and flower segments.
trilobite (n.) Look up trilobite at Dictionary.com
extinct marine arthropod, 1820, 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.) Look up trilogy at Dictionary.com
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.) Look up trim at Dictionary.com
mid-15c., probably from Old English trymian, trymman "strengthen, fortify, confirm; comfort; incite; set in order, arrange, prepare, make ready; become strong," from trum "strong, stable," from Proto-Germanic *trum-, from PIE *dru-mo-, suffixed form of *deru- "to be firm, solid, steadfast" (see true). Examples in Middle English are wanting.

Original sense is preserved in nautical phrase in fighting trim (see trim (n.)); where the verb meant "distribute the load of a ship so she floats on an even keel" (1570s). Meaning "make neat by cutting" is first recorded 1520s; that of "decorate, adorn" is from 1540s. Sense of "reduce" is attested from 1966.
trim (n.) Look up trim at Dictionary.com
"state of being prepared," 1580s, nautical jargon, "fit for sailing," from trim (v.). From 1570s as "ornament, decoration;" 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.
trim (adj.) Look up trim at Dictionary.com
c.1500, "neatly or smartly dressed," probably ultimately from trim (v.) or from related Old English trum "firm, fixed, secure, strong, sound, vigorous, active." Related: Trimly; trimness.
trimester (n.) Look up trimester at Dictionary.com
1821, "period of three months," from French trimestre (early 17c.), from Latin trimestris "of three months," from tri- "three" (see tri-) + mensis "month" (see moon (n.)). Specific obstetrics sense is attested from 1916. Related: Trimestrial.
trimeter (n.) Look up trimeter at Dictionary.com
"a verse of three metrical feet," 1560s, from Latin trimetrus, from Greek trimetros "having three measures," from tri- "three" (see tri-) + metron "a measure" (see meter (n.2)). Related: Trimetrical.
trimmer (n.) Look up trimmer at Dictionary.com
1550s, "one who trims," agent noun from trim (v.). Meaning "one who changes opinions, actions, etc. to suit circumstances" is from 1680s, from the verb in the nautical sense of "adjust the balance of sails or yards with reference to the wind's direction" (1620s).
trimmings (n.) Look up trimmings at Dictionary.com
"adornments, accessories, etc.," 1610s, from trim (v.).
trine (adj.) Look up trine at Dictionary.com
"threefold," late 14c., from Old French trine "triple, threefold" (13c.), from Latin trinus "threefold," from tres "three" (see three).
trinity (n.) Look up trinity at Dictionary.com
early 13c., "the Father, Son and Holy Spirit," constituting one God in prevailing Christian doctrine, from Old French trinite "Holy Trinity" (11c.), from Late Latin trinitatem (nominative trinitas) "Trinity, triad" (Tertullian), from Latin trinus "threefold, triple," from plural of trini "three at a time, threefold," related to tres (neuter tria) "three" (see three). The Latin word was widely borrowed in European languages with the rise of Christianity (Irish trionnoid, Welsh trindod, German trinität). Related: Trinitarian.
trinket (n.) Look up trinket at Dictionary.com
1530s, of unknown origin. Evidently a diminutive form, perhaps related to trick (n.).
trinomial (adj.) Look up trinomial at Dictionary.com
1670s, "having three names," from tri- + second element from binomial. In mathematics, "consisting of three terms" (1704).
trio (n.) Look up trio at Dictionary.com
1724, "composition for three voices," from French trio (c.1600), from Italian trio, from tri- "three" (see three); patterned on duo. Meaning "group of three persons" is from 1789.
triolet (n.) Look up triolet at Dictionary.com
verse form, from French triolet, a diminutive of trio (see trio).
trip (v.) Look up trip at Dictionary.com
late 14c., "tread or step lightly and nimbly, skip, dance, caper," from Old French triper "jump around, dance around, strike with the feet" (12c.), from a Germanic source (compare Middle Dutch trippen "to skip, trip, hop; to stamp, trample," Low German trippeln, Frisian tripje, Dutch trappen, Old English treppan "to tread, trample") related to trap (n.).

The senses of "to stumble" (intransitive), "strike with the foot and cause to stumble" (transitive) are from mid-15c. in English. Meaning "to release" (a catch, lever, etc.) is recorded from 1897; trip-wire is attested from 1868. Related: Tripped; tripping.
trip (n.) Look up trip at Dictionary.com
"act or action of tripping" (transitive), early 14c., from trip (v.); sense of "a short journey or voyage" is from mid-15c.; the exact connection to the earlier sense 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.) Look up tripartite at Dictionary.com
"divided in three," early 15c., from Latin tripartitus "divided into three parts," from tri- "three" (see three) + partitus, past participle of partiri "to divide" (see part (v.)).
tripe (n.) Look up tripe at Dictionary.com
c.1300, from Old French tripe "guts, intestines, entrails used as food" (13c.), of unknown origin, perhaps via Spanish tripa from Arabic therb "suet" [Klein, Barnhart]. Applied contemptuously to persons (1590s), then to anything considered worthless, foolish, or offensive (1892).
triple (v.) Look up triple at Dictionary.com
late 14c., from Medieval Latin triplare "to triple," from Latin triplus "threefold, triple," from tri- "three" (see tri-) + -plus "-fold" (see -plus). Related: Tripled; tripling.
triple (adj.) Look up triple at Dictionary.com
early 15c., from Old French triple or directly from Latin triplus (see triple (adj.)). As a noun, early 15c., "a triple sum or quantity," from the adjective. The baseball sense of "a three-base hit" is attested from 1880. Related: Triply (adv.). Triple-decker is from 1940 of sandwiches and wedding cakes, 1942 of beds.
triplet (n.) Look up triplet at Dictionary.com
1650s, "three successive lines of poetry," from triple; perhaps patterned on doublet. Extended to a set of three of anything by 1733, and to three children at the same birth by 1787 (another word for this was trin, 1831, on the model of twin). Musical meaning "three notes played in the time of two" is from 1801.
triplicate (adj.) Look up triplicate at Dictionary.com
early 15c., "triple, threefold," from Latin triplicatus, past participle of triplicare "to triple," from tri- "three" (see tri-) + plicare "to fold" see ply (v.1)).
triplicate (v.) Look up triplicate at Dictionary.com
"to multiply by three," 1620s, from Latin triplicatus (see triplicate (adj.)). Related: Triplicated; triplicating; triplication.
tripod (n.) Look up tripod at Dictionary.com
c.1600, "three-legged vessel," c.1600, from Latin tripus (genitive tripodis), from Greek tripous (genitive tripodos) "a three-legged stool or table," noun use of adjective meaning "three-footed," from tri- "three" (see tri-) + pous (genitive podos) "foot" (see foot (n.)). Related: Tripodal.
Tripoli Look up Tripoli at Dictionary.com
both the Libyan capital and the Lebanese port city represent Greek tri- "three" (see tri-) + polis "town" (see polis). In Libya, Tripolis was the name of a Phoenician colony consisting of Oea (which grew into modern Tripoli), Leptis Magna, and Sabratha. Arabic distinguishes them as Tarabulus ash-sham ("Syrian Tripoli") and Tarabulus al-garb ("Western Tripoli").
triptych (n.) Look up triptych at Dictionary.com
"three-part altar-piece carvings or pictures hinged together," 1849, based on Italian triptica, from tri- "three" on model of diptych.
trireme (n.) Look up trireme at Dictionary.com
"ancient ship with three rows of oars," c.1600, from Latin triremis, from tri- "three" (see tri-) + remus "oar" (see row (v.)).
Triscuit (n.) Look up Triscuit at Dictionary.com
proprietary name for a type of cracker, 1906, curiously from tri- + biscuit.
trisect (v.) Look up trisect at Dictionary.com
1690s, from tri- "three" + Latin sectus "cut," past participle of secare "to cut" (see section (n.)). Probably patterned on bisect. Related: Trisected; trisecting; trisection (1660s).
trisexual (adj.) Look up trisexual at Dictionary.com
by 1986, from tri- + sexual.