Online Etymology Dictionary

Thursday (n.): fifth day of the week, Old English þurresdæg, a contraction (perhaps influenced by Old Norse þorsdagr) of þunresdæg, literally "Thor's day," from Þunre, genitive of Þunor "Thor" (see thunder (n.)); from Proto-Germanic *thonaras daga (source also of Old Frisian thunresdei, Middle Dutch donresdach, Dutch donderdag, Old High German Donares tag, German Donnerstag, Danish and Swedish Torsdag "Thursday"), a loan-translation of Latin Jovis dies "day of Jupiter."

Roman Jupiter was identified with the Germanic Thor. The Latin word is the source of Italian giovedi, Old French juesdi, French jeudi, Spanish jueves, and is itself a loan-translation of Greek dios hemera "the day of Zeus."
thus (adv.): Old English þus "in this way, as follows," related to þæt "that" and this; from Proto-Germanic *thus- (source also of Old Saxon and Old Frisian thus, Middle Dutch and Dutch dus), from PIE *to-.
thusly (adv.): 1865 (in an Artemus Ward dialect humor piece), from thus + -ly (2). A double adverb. Perhaps originally a humorous or mocking over-correction of thus; it has gained some currency but earns frowns for the user.
thwack (v.): "to hit hard with a stick," 1520s, of echoic origin. Related: Thwacked; thwacking. The noun is recorded from 1580s.
thwaite (n.): "cleared land," 1620s, from Old Norse or Old Danish þveit "a clearing, meadow, paddock," literally "a cutting, cut-piece" (related to Old English þwitan "to cut, cut off;" see whittle). Always a rare word and now obsolete, but frequently encountered in place names, but "It is unclear whether the base meaning was 'something cut off, detached piece of land,' or 'something cut down, felled tree' ..." [Cambridge Dictionary of English Place-Names].
thwart (adv.): c. 1200, from a Scandinavian source, probably Old Norse þvert "across," originally neuter of thverr (adj.) "transverse, across," cognate with Old English þweorh "transverse, perverse, angry, cross," from Proto-Germanic *thwerh- "twisted, oblique" (source also of Middle Dutch dwers, Dutch dwars "cross-grained, contrary," Old High German twerh, German quer, Gothic þwairhs "angry"), altered (by influence of *thwer- "to turn") from *therkh-, from PIE *terkw- "to twist" (source also of Latin torquere "to twist," Sanskrit tarkuh "spindle," Old Church Slavonic traku "band, girdle," Old High German drahsil "turner," German drechseln "to turn on a lathe"), possibly a variant of *twerk- "to cut." From mid-13c. as an adjective.
thwart (v.): "oppose, hinder," mid-13c., from thwart (adv.). Related: Thwarted; thwarting.
thy (pron.): possessive pronoun of 2nd person singular, late 12c., reduced form of þin (see thine), until 15c. used only before consonants except -h-. Compare my/mine, a/an.
thyme (n.): plant of the mint family, late 14c., from Old French thym, tym (13c.) and directly from Latin thymum, from Greek thymon, from PIE *dheu- (1), base of words meaning "to rise in a cloud" (see fume (n.)); thus thyme might be the plant "having a strong odor," or it might be related to thyein "burn as a sacrifice," which would indicate the plant was used as incense. Related: Thymic.
thymine (n.): nitrogenous base, 1894, from German (Kossel and Neumann, 1893), from thymic acid, from which it was isolated, the acid so called because obtained from the thymus gland. With chemical suffix -ine (2).
thymus (n.): gland near the base of the neck, 1690s, Modern Latin, from Greek thymos "a warty excrescence," used of the gland by Galen, literally "thyme," probably so called because of a fancied resemblance to a bud of thyme (see thyme). Related: Thymic.
thyroid (adj.): 1690s (in reference to both the cartilage and the gland), from Greek thyreoiedes "shield-shaped" (in khondros thyreoiedes "shield-shaped cartilage," used by Galen to describe the "Adam's apple" in the throat), from thyreos "oblong, door-shaped shield" (from thyra "door," from PIE *dhwer-; see door) + -eides "form, shape" (see -oid). The noun, short for thyroid gland, is recorded from 1849.
thyroxine (n.): active principle of the thyroid gland, 1915, from thyro-, comb. form of thyroid, + oxy- (apparently a reference to the oxygen atom present in it, but OED has it as a shortening of oxy-indol) + chemical suffix -ine (2), denoting an amino acid.
thyrsus (n.): 1590s, from Latinized form of Greek thyrsos, literally "stalk or stem of a plant," a non-Greek word of unknown origin. The staff or spear, tipped with an ornament like a pine cone and sometimes wreathed in ivy and vine branches, borne by Dionysus and his votaries.
thyself (pron.): Middle English þi-self, from Old English þe self; see thy + self. One word from 16c. A pronoun used reflexively for emphasis after (or in place of) thou.
ti: seventh note of the musical scale, 1842, earlier te (1839), replacing si to avoid confusion with so, sol (see gamut).
Tia Maria (n.): coffee-flavored, rum-based liqueur, originally made in the West Indies, 1948, Spanish, literally "Aunt Mary."
tiara (n.): 1550s, "headdress of the Persian kings" (also worn by men of rank), from Latin tiara, from Greek tiara, of unknown origin. Earlier in Englished form tiar (1510s). As a richly jeweled headband in Western wear, 1650s (tiar; 1718 as tiara). Related: Tiaraed.
Tib: 1530s, typical name for an English woman of the lower class, hence "girl, lass, sweetheart," sometimes also "strumpet," from the pet form of Isabel. Often paired with Tom, as Jill was with Jack. Colloquial St. Tibb's Eve (1785) was the evening of the last day, the Day of Judgement, hence "never."
Tiber: river through Rome, likely from Celtic dubro "river" (compare Dover). Related: Tiburtine.
Tibert: name of the cat in "Reynard the Fox" (late 15c.), hence used as a proper name for any cat, from Flemish and Dutch Tybert, Old French Tibert. Identified with masc. proper name Tibalt, which is from Old French Thibauld, from Germanic *Theobald (see Theobald).
Tibet: said to be a corruption in Chinese or Arabic of Bod, indigenous name, of unknown origin. As an adjective in English, Tibetian is older (1747) but Tibetan (1822) is now the usual word. With comb. form Tibeto-.
tibia (n.): lower leg bone, 1726, from Latin tibia "shinbone," also "pipe, flute" (originally one of bone), in which sense it originally came into English (1540s). Of unknown origin. The Latin plural is tibiæ. Related: Tibial.
tic (n.): twitching of a facial muscle, 1822, often a shortening of tic douloureux "severe facial neuralgia," literally "painful twitch" (1798), from French tic "a twitching disease of horses" (17c.), of unknown origin. Klein suggests an imitative origin; Diez compare it to Italian ticchio "whim, caprice, ridiculous habit," itself of unknown origin.
tic douloureux (n.): 1798, French, literally "painful twitching;" see tic.
tick (n.1): parasitic blood-sucking arachnid animal, Old English ticia, from West Germanic *tik- (source also of Middle Dutch teke, Dutch teek, Old High German zecho, German Zecke "tick"), of unknown origin, perhaps from PIE *deigh- "insect." French tique (mid-15c.), Italian zecca are Germanic loan-words.
tick (n.2): mid-15c., "light touch or tap," probably from tick (v.) and cognate with Dutch tik, Middle High German zic, and perhaps echoic. Meaning "sound made by a clock" is probably first recorded 1540s; tick-tock as the sound of a clock is recorded from 1845.
tick (n.3): "credit," 1640s, shortening of ticket (n.).
tick (v.): early 13c., "to touch or pat," perhaps from an Old English verb corresponding to tick (n.2), and perhaps ultimately echoic. Compare Old High German zeckon "to pluck," Dutch tikken "to pat," Norwegian tikke "touch lightly." Meaning "make a ticking sound" is from 1721. Related: Ticked; ticking.

To tick (someone) off is from 1915, originally "to reprimand, scold." The verbal phrase tick off was in use in several senses at the time: as what a telegraph instrument does when it types out a message (1873), as what a clock does in marking the passage of time (1777), to enumerate on one's fingers (1899), and in accountancy, etc., "make a mark beside an item on a sheet with a pencil, etc.," often indicating a sale (by 1881, from tick (n.2) in sense "small mark or dot"). This last might be the direct source of the phrase, perhaps via World War I military bureaucratic sense of being marked off from a list as "dismissed" or "ineligible." Meaning "to annoy" is recorded by 1971.
tick-tack-toe (n.): children's three-in-a-row game with Xs and Os, so called by 1892, earlier tit-tat-toe (by 1852, in reminiscences of earlier years), also called noughts and crosses (1852). Probably from the sound of the pencil on the slate with which it originally was played by schoolboys. Also the name of a children's counting rhyme played on slate (also originally tit-tat-toe, by 1842), and compare tick-tack (1580s), a form of backgammon, possibly from Middle French trictrac, perhaps imitative of the sound of tiles on the board.
ticker (n.): 1821, "something that ticks," agent noun from tick (v.); slang meaning "heart" first recorded 1930. Ticker tape (1891) is from ticker "telegraphic device for recording stock market quotations, etc." (1883).
ticket (v.): 1610s, "attach a ticket to, put a label on," from ticket (n.). Meaning "issue a (parking) ticket to" is from 1955. Related: Ticketed; ticketing.
ticket (n.): 1520s, "short note or document," from a shortened form of Middle French etiquet "label, note," from Old French estiquette "a little note" (late 14c.), especially one affixed to a gate or wall as a public notice, literally "something stuck (up or on)," from estiquer "to affix, stick on, attach," from Frankish *stikkan, cognate with Old English stician "to pierce," from Proto-Germanic *stikken "to be stuck," stative form from PIE *steig- "to stick; pointed" (see stick (v.)).

Meaning "card or piece of paper that gives its holder a right or privilege" is first recorded 1670s, probably developing from the sense of "certificate, licence, permit." The political sense of "list of candidates put forward by a faction" has been used in American English since 1711. Meaning "official notification of offense" is from 1930. Big ticket item is from 1953. Slang the ticket "just the thing, what is expected" is recorded from 1838, perhaps with notion of a winning lottery ticket.
ticking (n.): "cloth covering (usually of strong cotton or linen) for mattresses or pillows," 1640s, from tyke (modern tick) with the same meaning (mid-14c.), probably from Middle Dutch tike, from a West Germanic borrowing of Latin theca "case," from Greek theke "a case, box, cover, sheath" (see theco-).
tickle (v.): c. 1300 (implied in tickling) "to touch lightly so as to cause a peculiar and uneasy or thrilling sensation in the nerves," of uncertain origin, possibly a frequentative form of tick (v.) in its older sense of "to touch." Some suggest a metathesis of Middle English kittle, which is from a shared Germanic word for "to tickle," but tickle is attested earlier. The Old English form was tinclian.

Meaning "to excite agreeably" (late 14c.) is a translation of Latin titillare. Meaning "to poke or touch so as to excite laughter" is from early 15c.; figurative sense of "to excite, amuse" is attested from 1680s. The noun is recorded from 1801. To tickle (one's) fancy is from 1640s. Related: Tickler.
tickled (adj.): "pleased, happy," 1580s, past participle adjective from tickle (v.). To be tickled pink is from 1909.
ticklish (adj.): "easily tickled," 1590s, from tickle + -ish. Literal sense is attested later than the figurative sense "easy to upset" (1580s). An earlier word for this was tickly (1520s). Meaning "difficult to do, dubious, requiring great care" is from 1590s. Related: Ticklishly; ticklishness.
ticky-tacky (n.): "inferior, cheap material," 1962 (in song "Little Boxes" by U.S. political folk-singer Malvina Reynolds, 1900-1978), reduplication of tacky. As an adjective by 1967.
Ticonderoga: place in New York state, from Mohawk (Iroquoian) tekotaro:ke "branching (or confluence) of waters," with -otar- "large river, lake."
tidal (adj.): 1807, a hybrid formation from tide (n.) + Latin-derived suffix -al (1). A tidal wave (1819) properly is high water caused by movements of the tides; erroneous use for "tsunami, great ocean wave caused by an earthquake, etc." is recorded from 1868.
tidbit (n.): 1630s, probably from dialectal tid "fond, solicitous, tender" (perhaps by influence of tit (n.2)) + bit (n.1) "morsel."
tiddlywinks (n.): children's tile-flipping game, 1857, probably an arbitrary formation from baby talk, but perhaps from slang tiddly-wink "unlicensed drink shop" (1844), from slang tiddly "a drink, drunk."
tide (n.): Old English tid "point or portion of time, due time, period, season; feast-day, canonical hour," from Proto-Germanic *tidiz "division of time" (source also of Old Saxon tid, Dutch tijd, Old High German zit, German Zeit "time"), from PIE *di-ti- "division, division of time," suffixed form of root *da- "to divide, cut up" (source also of Sanskrit dati "cuts, divides;" Greek demos "people, land," perhaps literally "division of society," daiesthai "to divide;" Old Irish dam "troop, company").

Meaning "rise and fall of the sea" (mid-14c.) probably is via notion of "fixed time," specifically "time of high water;" either a native evolution or from Middle Low German getide (compare Middle Dutch tijd, Dutch tij, German Gezeiten "flood tide, tide of the sea"). Old English seems to have had no specific word for this, using flod and ebba to refer to the rise and fall. Old English heahtid "high tide" meant "festival, high day."
tide (v.): "to carry (as the tide does)," 1620s, from tide (n.). Usually with over. Earlier it meant "to happen" (Old English; see tidings). Related: Tided; tiding.
tidewater (n.): also tide-water, 1772, "water affected by the normal ebb and flow of the tide," from tide (n.) + water (n.1). In reference to the lowland regions of the Virginia shore of the western Chesapeake Bay, 1832.
tidings (n.): "announcement of an event," c. 1200, from late Old English tidung "event, occurrence, piece of news," verbal noun from Old English tidan "to happen," or in part from Old Norse tiðendi (plural) "events, news," from tiðr (adj.) "occurring," from PIE *di-ti- (see tide (n.)). Similar formation in Norwegian tidende "tidings, news," Dutch tijding, German Zeitung "newspaper."
tidy (adj.): mid-13c., "in good condition, healthy," probably originally "in season, timely, opportune, excellent" (though this sense is not attested until mid-14c.), from tide (n.) in the sense of "season, time" + -y (2). Of persons, "of neat and orderly habits," from 1706. Similar formation in Old High German zitig, German zeitig, Dutch tijdig, Danish tidig "timely," Old English tidlic "temporal," also "timely, seasonable."
tidy (v.): "to make neat, set in order," 1821, from tidy (adj.). Related: Tidied; tidying.
tie (n.): Old English teag, "cord, band, thong, fetter," literally "that with which anything is tied," from Proto-Germanic *taugo (source also of Old Norse taug "tie," tygill "string"), from PIE *deuk- "to pull, to lead" (source also of Old English teon "to draw, pull, drag;" see duke (n.)).

Figurative sense is recorded from 1550s. Sense of "cravat, necktie" (usually a simple one knotted in front) first recorded 1761. The railway sense of "cross-beam between and beneath rails to keep them in place" is from 1857, American English. Meaning "equality between competitors" is first found 1670s, from notion of a connecting link. Tie-breaker is recorded from 1938.
tie (v.): Old English tigan, tiegan "to tie, bind, join, connect," from the source of tie (n.). Meaning "to finish equal to a competitor" is from 1888. Related: Tied; tying. To tie the knot in the figurative sense "form a union" is from 1707. Tie one on "get drunk" is recorded from 1944.