thumbnail (n.) Look up thumbnail at Dictionary.com
c.1600, from thumb (n.) + nail (n.). Meaning "drawing or sketch of a small size" (though usually not literally the size of a thumbnail) is from 1852.
thumbtack (n.) Look up thumbtack at Dictionary.com
tack with a broad, flat head which may be driven by pressure from the thumb, 1884, from thumb (n.) + tack (n.1).
thump (v.) Look up thump at Dictionary.com
1530s, "to strike hard," probably imitative of the sound made by hitting with a heavy object (compare East Frisian dump "a knock," Swedish dialectal dumpa "to make a noise"). Related: Thumped; thumping.
thump (n.) Look up thump at Dictionary.com
1550s, "dull, heavy sound," from thump (v.). As "a hard blow" from 1620s.
thumping (adj.) Look up thumping at Dictionary.com
"exceptionally large," colloquial, 1570s, present participle adjective from thump (v.).
thunder (n.) Look up thunder at Dictionary.com
mid-13c., from Old English þunor "thunder, thunderclap; the god Thor," from Proto-Germanic *thunraz (cognates: Old Norse þorr, Old Frisian thuner, Middle Dutch donre, Dutch donder, Old High German donar, German Donner "thunder"), from PIE *(s)tene- "to resound, thunder" (cognates: Sanskrit tanayitnuh "thundering," Persian tundar "thunder," Latin tonare "to thunder"). Swedish tordön is literally "Thor's din." The intrusive -d- also is found in Dutch and Icelandic versions of the word. Thunder-stick, imagined word used by primitive peoples for "gun," attested from 1904.
thunder (v.) Look up thunder at Dictionary.com
13c., from Old English þunrian, from the source of thunder (n.). Figurative sense of "to speak loudly, threateningly, or bombastically" is recorded from mid-14c. Related: Thundered; thundering. Compare Dutch donderen, German donnern.
thunderbird (n.) Look up thunderbird at Dictionary.com
legendary cause of thunder in many Native American cultures, 1848, a translation of native words, such as Ojibwa (Algonquian) aninikii, Lakotah (Siouan) wakiya, Klamath /lmelmnis/. See thunder (n.) + bird (n.1). In Lakhota, "the thunderbirds call" is "the usual expression for thunder" [Bright].
thunderbolt (n.) Look up thunderbolt at Dictionary.com
mid-15c., from thunder (n.) + bolt (n.) "arrow, projectile."
thunderclap (n.) Look up thunderclap at Dictionary.com
also thunder-clap, late 14c., from thunder (n.) + clap (n.1).
thunderhead (n.) Look up thunderhead at Dictionary.com
"high-piled cumulus cloud," one likely to develop into a thunderstorm, 1861, from thunder (n.) + head (n.).
thunderous (adj.) Look up thunderous at Dictionary.com
1580s, from thunder (n.) + -ous. Related: Thunderously.
thunderstorm (n.) Look up thunderstorm at Dictionary.com
also thunder-storm, 1560s, from thunder (n.) + storm (n.).
thunderstruck (adj.) Look up thunderstruck at Dictionary.com
1610s, from thunder (n.) + struck. Originally figurative; the literal sense (1630s) always has been rare. Thunder-strike (v.), is a back-formation.
thunk (n.) Look up thunk at Dictionary.com
sound of impact, attested from 1952, echoic.
thunk (v.) Look up thunk at Dictionary.com
dialectal or jocular past tense or past participle of think, by 1876. Not historical, but by analogy of drink/drunk, sink/sunk, etc.
Thuringia Look up Thuringia at Dictionary.com
region in Germany, German Thüringen, named for the ancient Thoringi people.
Thursday (n.) Look up Thursday at Dictionary.com
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 (cognates: 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.) Look up thus at Dictionary.com
Old English þus "in this way, as follows," related to þæt "that" and this; from Proto-Germanic *thus- (cognates: Old Saxon and Old Frisian thus, Middle Dutch and Dutch dus), from PIE *to-.
thusly (adv.) Look up thusly at Dictionary.com
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.) Look up thwack at Dictionary.com
"to hit hard with a stick," 1520s, of echoic origin. Related: Thwacked; thwacking. The noun is recorded from 1580s.
thwaite (n.) Look up thwaite at Dictionary.com
"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.) Look up thwart at Dictionary.com
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" (cognates: 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" (cognates: 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.) Look up thwart at Dictionary.com
"oppose, hinder," mid-13c., from thwart (adv.). Related: Thwarted; thwarting.
thy (pron.) Look up thy at Dictionary.com
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.) Look up thyme at Dictionary.com
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.) Look up thymine at Dictionary.com
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.) Look up thymus at Dictionary.com
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.) Look up thyroid at Dictionary.com
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.) Look up thyroxine at Dictionary.com
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.) Look up thyrsus at Dictionary.com
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.) Look up thyself at Dictionary.com
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 Look up ti at Dictionary.com
seventh note of the musical scale, 1842, earlier te (1839), replacing si to avoid confusion with so, sol (see gamut).
Tia Maria (n.) Look up Tia Maria at Dictionary.com
coffee-flavored, rum-based liqueur, originally made in the West Indies, 1948, Spanish, literally "Aunt Mary."
tiara (n.) Look up tiara at Dictionary.com
1550s, "headdress of the Persian kings" (also worn by men of rank), from Latin tiara, from Greek tiara, of unknown origin. Earlier in anglicized form tiar (1510s). As a richly jeweled headband in Western wear, 1650s (tiar; 1718 as tiara). Related: Tiaraed.
Tib Look up Tib at Dictionary.com
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 Look up Tiber at Dictionary.com
river through Rome, likely from Celtic dubro "river" (compare Dover). Related: Tiburtine.
Tibert Look up Tibert at Dictionary.com
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 Look up Tibet at Dictionary.com
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.) Look up tibia at Dictionary.com
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.) Look up tic at Dictionary.com
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.) Look up tic douloureux at Dictionary.com
1798, French, literally "painful twitching;" see tic.
tick (n.1) Look up tick at Dictionary.com
parasitic blood-sucking arachnid animal, Old English ticia, from West Germanic *tik- (cognates: 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) Look up tick at Dictionary.com
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 (v.) Look up tick at Dictionary.com
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 (n.3) Look up tick at Dictionary.com
"credit," 1640s, shortening of ticket (n.).
tick-tack-toe (n.) Look up tick-tack-toe at Dictionary.com
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.) Look up ticker at Dictionary.com
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 (n.) Look up ticket at Dictionary.com
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, license, 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.
ticket (v.) Look up ticket at Dictionary.com
1610s, "attach a ticket to, put a label on," from ticket (n.). Meaning "issue a (parking) ticket to" is from 1955. Related: Ticketed; ticketing.