Online Etymology Dictionary

trade (n.): late 14c., "path, track, course of action," introduced by the Hanse merchants, from Middle Dutch or Middle Low German trade "track, course" (probably originally of a trading ship), cognate with Old English tredan (see tread). Sense of "one's habitual business" (1540s) developed from the notion of "way, course, manner of life" (mid-15c.); sense of "buying and selling" is first recorded 1550s. Trade wind (1640s) has nothing to do with commerce, but preserves the obsolete sense of "in a habitual or regular course." Trade union is attested from 1831.
trade (v.): 1540s, "to tread a path," from trade (n.). Meaning "to occupy oneself (in something)" is recorded from c.1600. The U.S. sports team sense of "to exchange one player for another" is attested from 1899. Related: Traded; trading. To trade down is attested from 1942. Trade-in in reference to used cars is recorded from 1917. Trading post is recorded from 1796.
trademark (n.): 1838 (the thing itself attested continuously from 14c.), from trade (n.) + mark (n.1). Figurative use by 1869. As a verb, from 1904. Related: Trademarked; trademarking.
tradeoff (n.): also trade-off, "sacrifice of one benefit for another," 1959, from verbal phrase to trade off; see trade + off.
tradition (n.): late 14c., from Old French tradicion (late 13c.), from Latin traditionem (nominative traditio) "delivery, surrender, a handing down," from traditus, past participle of tradere "deliver, hand over," from trans- "over" (see trans-) + dare "to give" (see date (n.1)). The word is a doublet of treason (q.v.). The notion in the modern sense of the word is of things "handed down" from generation to generation.
traditional (dj.): c.1600, from tradition + -al (1). In reference to jazz, from 1950. Slang trad, short for trad(itional jazz) is recorded from 1956; its general use for "traditional" is recorded from 1963. Related: Traditionally.
traduce (v.): 1530s, "to alter, change over, transport," from Latin traducere "change over, convert," originally "lead along or across, transfer," from trans- "across" (see trans-) + ducere "to lead" (see duke (n.)). Sense of "defame, slander" (1580s) is from Latin traducere in the sense of "to scorn or disgrace," probably from the notion of "to lead along as a spectacle." Related: Traduced; traducing.
traffic (n.): c.1500, "trade, commerce," from Middle French trafique (mid-15c.), from Italian traffico (early 14c.), from trafficare "carry on trade," of uncertain origin, perhaps from a Vulgar Latin *transfricare "to rub across" (from Latin trans- "across" + fricare "to rub"), with the original sense of the Italian verb being "touch repeatedly, handle."

Or the second element may be an unexplained alteration of Latin facere "to make, do." Klein suggests ultimate derivation of the Italian word from Arabic tafriq "distribution." Meaning "people and vehicles coming and going" first recorded 1825. Traffic jam is 1917, ousting earlier traffic block (1895).
traffic (v.): 1540s, from traffic (n.) and preserving the original commercial sense. Related: Trafficked; trafficking. The -k- is inserted to preserve the "k" sound of -c- before a suffix beginning in -i-, -y-, or -e- (cf. picnic/picnicking, panic/panicky, shellac/shellacked).
tragedian (n.): "writer of tragedies," late 14c., from Old French tragediane (Modern French tragédien), from tragedie (see tragedy). Another word for this was tragician (mid-15c.).
tragedy (n.): late 14c., "play or other serious literary work with an unhappy ending," from Old French tragedie (14c.), from Latin tragedia "a tragedy," from Greek tragodia "a dramatic poem or play in formal language and having an unhappy resolution," apparently literally "goat song," from tragos "goat" + oide "song." The connection may be via satyric drama, from which tragedy later developed, in which actors or singers were dressed in goatskins to represent satyrs. But many other theories have been made (including "singer who competes for a goat as a prize"), and even the "goat" connection is at times questioned. Meaning "any unhappy event, disaster" is from c.1500.
tragic (adj.): 1540s, "calamitous, disastrous, fatal," shortened from tragical (late 15c.), modeled on Latin tragicus, from Greek tragikos "of or pertaining to tragedy," literally "of or pertaining to a goat," and probably referring to a satyr impersonated by a goat singer or satyric actor (see tragedy). Tragic flaw (1913) translates Greek hamartia.
tragicomedy (n.): 1570s, from Middle French tragicomédie (1540s), from Italian tragicommedia, from Late Latin tragicomoedia (c.325), contraction of tragicocomoedia (Plautus), from tragicus (see tragic) + comoedia (see comedy).
tragus (n.): "eminence at the opening of the ear," 1690s, Modern Latin, from Greek tragos, properly "he-goat;" so called for the tuft of hair which grows there, which resembles a goat's beard.
trail (v.): c.1300, "to hang down loosely and flow behind," from Old French trailler "to tow," ultimately from Vulgar Latin *tragulare "to drag," from Latin tragula "dragnet," probably related to trahere "to pull" (see tract (n.1)). The meaning "follow the trail of" (an animal, etc.) is first recorded late 14c. Related: Trailed; trailing.
trail (n.): early 14c., "trailing part of a robe, gown, etc.," from the source of trail (v.). The meaning "track or smell left by a person or animal" is also from 1580s. Meaning "path or track worn in wilderness" is attested from 1807.
Trail of Tears: in reference to the U.S. government's brutally incompetent Cherokee removal of 1838-9, attested by 1908.
trailblazer (n.): by 1893, from trail (n.) + agent noun from blaze (2).
trailer (n.): 1890, "vehicle pulled by another," agent noun from trail (v.); originally a small carriage drawn along by a bicycle. Meaning "preview of a coming movie" first attested 1928. Trailer park recorded by 1936. Trailer trash in use by 1986.
train (n.): early 14c., "a drawing out, delay," later "trailing part of a skirt" (mid-15c.), also "retinue, procession" (mid-15c.), from Old French train (fem. traine), from trainer "to pull, draw," from Vulgar Latin *traginare, extended from *tragere "to pull," back-formation from tractus, past participle of Latin trahere "to pull, draw" (see tract (n.1)).

Train of thought first attested 1650s. The railroad sense is recorded from 1820 (publication year, dated 1816), from notion of a "train" of wagons or carriages pulled by a mechanical engine.
train (v.): "instruct, discipline, teach," 1540s, probably from earlier sense of "draw out and manipulate in order to bring to a desired form" (late 14c.), specifically of the growth of branches, vines, etc. from mid-15c.; from train (n.). The meaning "to travel by railway" is recorded from 1856. Related: Trained; training.
trainee (n.): 1841, from train (v.) + -ee.
trainer (n.): c.1600, agent noun from train (v.).
trainspotting (n.): 1959 (train spotter attested from 1958), chiefly British English, in reference to the hobby of recording the numbers of the locomotives one has observed; see train (n.) in the railroad sense + spot (v.).
traipse (v.): 1590s, of uncertain origin, perhaps from dialectal French trepasser "pass over or beyond," from Old French trespasser (see trespass). Or from a source related to Middle Dutch trappen, dialectal Norwegian trappa "to tread, stamp" (see trap). Liberman points out that it resembles German traben "tramp" "and other similar verbs meaning 'tramp; wander; flee' in several European languages. They seem to have been part of soldiers' and vagabonds' slang between 1400 and 1700. In all likelihood, they originated as onomatopoeias and spread to neighboring languages from Low German." Related: Traipsed; traipsing.
trait (n.): late 15c., "shot, missiles;" later "a stroke, short line" (1580s), from Middle French trait, from Latin tractus "draft, drawing, drawing out," later "line drawn, feature," from past participle stem of trahere "to pull, draw" (see tract (n.1)). Sense of "particular feature, distinguishing quality" is first recorded 1752, from meaning "line, streak, feature" (1560s), which is common to English, French, and Latin.
traitor (n.): c.1200, from Old French traitor (11c.), from Latin traditorem (nominative traditor) "betrayer," literally "one who delivers," from stem of tradere "deliver, surrender" (see tradition). Originally usually with a suggestion of Judas Iscariot.
traitorous (adj.): late 14c., apparently from Old French traitreus (mid-13c.), from traitor (see traitor).
trajectory (n.): 1690s, from Modern Latin trajectoria, from fem. of trajectorius "of or pertaining to throwing across," from Latin traiectus "thrown over or across," past participle of traicere "throw across," from Latin trans- "across" (see trans-) + icere, combining form of iacere "to throw" (see jet (v.)). Used in Late Latin and Middle English to mean "a funnel."
tram (n.): c.1500, "beam or shaft of a barrow or sledge," also "a barrow or truck body" (1510s), Scottish, originally in reference to the iron trucks used in coal mines, probably from Middle Flemish tram "beam, handle of a barrow, bar, rung," a North Sea Germanic word of unknown origin. The sense of "track for a barrow, tramway" is first recorded 1826; that of "streetcar" is first recorded 1860. Tram-car is attested from 1873.
trammel (n.): mid-14c. (implied in trammeller) "net to catch fish," from Middle French tramail, from Old French (early 13c.), from Late Latin tremaculum, perhaps meaning "a net made from three layers of meshes," from Latin tri- "three" + macula "a mesh" (see mail (2)). Italian tramaglio, Spanish trasmallo are French loan-words.
trammel (v.): 1530s, originally "to bind up (a corpse);" sense of "hinder, restrain" is from 1727, from trammel (n.). Related: Trammeled; trammeling.
tramp (n.): "person who wanders about, vagabond," 1660s, from tramp (v). Sense of "steamship which takes cargo wherever it can be traded" (as opposed to one running a regular line) is attested from c.1880. The meaning "promiscuous woman" is from 1922.
tramp (v.): late 14c., "walk heavily, stamp," from Middle Low German trampen "to stamp," from Proto-Germanic *tramp- (cf. Danish trampe, Swedish trampa "to tramp, stamp," Gothic ana-trimpan "to press upon"), probably from a variant of the Proto-Germanic source of trap. Related: Tramped; tramping.
trample (v.): late 14c., "to walk heavily," frequentative form of tramp. Transitive sense is first found 1520s. Related: Trampled; trampling.
trampoline (n.): 1798, from Spanish trampolin "springboard," and Italian trampolino, from trampoli "stilts," from a Germanic source (cf. Low German trampeln "trample") related to tramp.
trance (n.): late 14c., "state of extreme dread or suspense," also "a dazed, half-conscious or insensible condition," from Old French transe "fear of coming evil," originally "passage from life to death" (12c.), from transir "be numb with fear," originally "die, pass on," from Latin transire "cross over" (see transient). French trance in its modern sense has been reborrowed from English.
tranche (n.): c.1500, from French tranche, from trancher, trencher "to cut" (see trench). Economic sense is from 1930.
tranquil (adj.): mid-15c., from Latin tranquillus "quiet" (see tranquility). Related: Tranquilly.
tranquility (n.): also tranquillity, late 14c., from Old French tranquilite (12c.), from Latin tranquillitatem (nominative tranquillitas) "tranquilness," from tranquillus "tranquil," perhaps from trans- "over" (here in its intensive sense of "exceedingly") + a root related to quies "rest" (see quiet (n.)).
tranquilize (v.): 1620s, from tranquil + -ize. Related: Tranquilized; tranquilizing.
tranquilizer (n.): "sedative," 1824 (first reference is to ground ivy), agent noun from tranquilize; in reference to one of a large group of anti-anxiety drugs, it is recorded by 1956.
trans-: prefix meaning "across, beyond, to go beyond," from Latin trans-, from prep. trans "across, over, beyond," probably originally present participle of a verb *trare-, meaning "to cross" (see through).
trans-Atlantic: allso transatlantic, 1779, from trans- "through, across" + Atlantic.
trans-oceanic (adj.): 1827, "situated across the ocean," from trans- + oceanic. Meaning "passing over the sea" is recorded from 1868.
transact (v.): 1580s, from Latin transactus, past participle of transigere "to drive through, accomplish" (see transaction). Related: Transacted; transacting.
transaction (n.): mid-15c., "the adjustment of a dispute, a negotiated agreement," from Middle French transaction, from Latin transactionem (nominative transactio) "an agreement, accomplishment," from past participle stem of transigere "accomplish, drive or carry through," from trans- "through" + agere "to drive" (see act). Meaning "a piece of business" is attested from 1640s.
transaxle (n.): 1958, from transmission axle.
transceiver (n.): 1934, from a merger of transmitter + receiver.
transcend (v.): mid-14c., from Latin transcendere "climb over or beyond, surmount," from trans- "beyond" (see trans-) + scandere "to climb" (see scan (v.)). Related: Transcended; transcending.