thanksgiving (n.) Look up thanksgiving at Dictionary.com
1530s, "the giving of thanks," from thanks (n.) + present participle of give (v.). In the specific sense of "public celebration acknowledging divine favors" thanksgiving dates from 1630s (the first one in America was held October 1621 by Plymouth Colony Pilgrims in appreciation of assistance from members of the Massasoit tribe and celebration of the first harvest); though Thanksgiving Day itself is not attested until 1670s.
that (pron.) Look up that at Dictionary.com
Old English þæt, neuter singular of the demonstrative pronoun and adjective (corresponding to masc. se, fem. seo), from Proto-Germanic *that, from PIE *tod-, extended form of demonstrative pronomial base *to- (cf. Sanskrit ta-, Lithuanian and Old Church Slavonic to, Greek to "the," Latin talis "such"). Cf. the.

Emerged c.1200 as a demonstrative adjective with the breakdown of the Old English grammatical gender system, perhaps by influence of French and Latin, which had demonstrative adjectives (Old English did not). Slang that way "in love" first recorded 1929. That-a-way is recorded from 1839. "Take that!" said while delivering a blow, is recorded from early 15c.
thatch (v.) Look up thatch at Dictionary.com
Old English þeccan "to cover," related to þæc "roof, thatching material," from Proto-Germanic *thakan (cf. Old Saxon thekkian, Old Norse þekja, Old Frisian thekka, Middle Dutch decken, Old High German decchen, German decken "to cover"), from PIE *(s)tog-/*(s)teg- "cover" (see stegosaurus).
thatch (n.) Look up thatch at Dictionary.com
Old English þæc "roof, thatch," from the source of thatch (v.). Cf. Old Norse þak, Old Frisian thek, Middle Dutch dak "roof," Old High German dah, German Dach "roof."
thatcher (n.) Look up thatcher at Dictionary.com
early 14c. (late 12c. as a surname); agent noun from thatch (v.).
thaught (n.) Look up thaught at Dictionary.com
"rower's bench," 1620s, alteration of thoft, from Old English þofte, from Proto-Germanic *thufto- (cf. Dutch doft, German ducht), from PIE *tupta-, from root *tup- "to squat."
thaumaturge (n.) Look up thaumaturge at Dictionary.com
1620s (implied in thaumaturgical), from Modern Latin, from Greek thaumatourgos "wonder-working, conjurer," from thauma (genitive thaumatos) "wonder, wonderous thing," prop. "a thing to look at" (from root of theater, q.v.) + ergon "work" (see urge (v.)).
thaumaturgy (n.) Look up thaumaturgy at Dictionary.com
1727, from Greek thaumatourgia, from thaumatourgos (see thaumaturge).
thaw (n.) Look up thaw at Dictionary.com
c.1400, from thaw (v.). Figurative sense of "relaxation of political harshness or hostility" is recorded from 1950, an image from the "Cold War."
thaw (v.) Look up thaw at Dictionary.com
Old English þawian, from Proto-Germanic *thawojanan (cf. Old Norse þeyja, Middle Low German doien, Dutch dooien, Old High German douwen, German tauen "to thaw"), from PIE root *ta- "to melt, dissolve" (cf. Sanskrit toyam "water," Ossetic thayun "to thaw," Welsh tawadd "molten," Doric Greek takein "to melt, waste, be consumed," Old Irish tam "pestilence," Latin tabes "a melting, wasting away, putrefaction," Old Church Slavonic tajati "to melt"). Related: Thawed; thawing.
thc (n.) Look up thc at Dictionary.com
active ingredient in marijuana and hashish, 1968, short for tetrahydrocannabinol (1940).
the Look up the at Dictionary.com
late Old English þe, nominative masculine form of the demonstrative pronoun and adjective. After c.950, it replaced earlier se (masc.), seo (fem.), þæt (neuter), and probably represents se altered by the þ- form which was used in all the masculine oblique cases (see below).

Old English se is from PIE root *so- "this, that" (cf. Sanskrit sa, Avestan ha, Greek ho, he "the," Irish and Gaelic so "this"). For the þ- forms, see that.

The s- forms were entirely superseded in English by mid-13c., excepting dialectal survival slightly longer in Kent. Old English used 10 different words for "the" (see table, below), but did not distinguish "the" from "that." That survived for a time as a definite article before vowels (cf. that one or that other).

Adverbial use in the more the merrier, the sooner the better, etc. is a relic of Old English þy, originally the instrumentive case of the neuter demonstrative þæt (see that).

Masc. Fem. Neut. Plural
Nom. se seo þæt þa
Acc. þone þa þæt þa
Gen. þæs þære þæs þara
Dat. þæm þære þæm þæm
Inst. þy, þon -- þy, þon --
Thea Look up Thea at Dictionary.com
fem. proper name, from Greek thea "goddess," fem. equivalent of theos "god," from PIE root *dhes-, root of words applied to various religious concepts, e.g. Latin feriae "holidays," festus "festive," fanum "temple."
theater (n.) Look up theater at Dictionary.com
late 14c., "open air place in ancient times for viewing spectacles," from Old French theatre (12c.), from Latin theatrum, from Greek theatron "theater," literally "place for viewing," from theasthai "to behold" (cf. thea "a view," theates "spectator") + -tron, suffix denoting place. Meaning "building where plays are shown" (1570s) was transferred to that of "plays, writing, production, the stage" (1660s). Spelling with -re prevailed in Britain after c.1700, but American English retained or revived the older spelling in -er. Generic sense of "place of action" is from 1580s; especially "region where war is being fought" (1914).
The Theatre of the Absurd strives to express its sense of the senselessness of the human condition and the inadequacy of the rational approach by the open abandonment of rational devices and discursive thought. [M. Esslin, "Theatre of the Absurd," 1961]
theatre (n.) Look up theatre at Dictionary.com
chiefly British English spelling of theater (q.v.); for spelling, see -re.
theatrical (adj.) Look up theatrical at Dictionary.com
1550s, "pertaining to the theater," from theater + -ical. Sense of "stagy, histrionic" is attested from 1709.
theatrics (n.) Look up theatrics at Dictionary.com
1807, "matters pertaining to the stage," from theater; also see -ics. Meaning "theatrical behavior" is attested from 1929, American English.
Thebaid (n.) Look up Thebaid at Dictionary.com
1727, "district around Thebes (in Egypt)," formerly haunted by hermits and ascetics. Also, "pertaining to (Boeotian) Thebes" in Greece, especially in reference to the poem by Statius.
theco- Look up theco- at Dictionary.com
word-forming element used in botany and zoology, from combining form of Greek theke "case, receptacle," from root of tithenai "to put, place" (see theme).
thee Look up thee at Dictionary.com
Old English þe (accusative and dative singular of þu "thou"), from Proto-Germanic *theke (cf. Old Frisian thi, Middle Dutch di, Old High German dih, German dich, Old Norse þik, Norwegian deg, Gothic þuk), from PIE *tege-. A brief history of the second person pronoun in English can be found here. The verb meaning "to use the pronoun 'thee' to someone" is recorded from 1662, from the rise of Quakerism (see thou).
This was the Bottom upon which the Quakers first set up, to run down all worldly Honour ...; to Thee and Thou; to call no Man Master, or Lord, and not to take off their Hats, or Bow to any. [Charles Leslie, "The Snake in the Grass," 1696]
theft (n.) Look up theft at Dictionary.com
Old English þeofð (West Saxon þiefð), from Proto-Germanic *theubitho (cf. Old Frisian thiufthe, Old Norse þyfð), from *theubaz "thief" (see thief) + suffix -itha (cognate with Latin -itatem).
thegn (n.) Look up thegn at Dictionary.com
"military tenant of an Anglo-Saxon king," a modern revival first attested 1848; see thane.
their Look up their at Dictionary.com
c.1200, from Old Norse þierra, genitive of þeir "they" (see they). Replaced Old English hiera. Use with singular objects, scorned by grammarians, is attested from c.1300. Theirs (c.1300) is a double possessive. Alternative form theirn (1836) is attested in Midlands and southern dialect in U.K. and the Ozarks region of the U.S.
theirself Look up theirself at Dictionary.com
c.1300, variant of themself, with self, originally an inflected adjective, treated as a noun with a meaning "person." Related: Theirselves.
theism (n.) Look up theism at Dictionary.com
"belief in a deity," 1670s; see theist. Meaning "belief in one god" (as opposed to polytheism) is recorded from 1711.
theist (n.) Look up theist at Dictionary.com
1660s, from Greek theos "god" (see Thea) + -ist. The original senses was that later reserved to deist: "one who believes in a transcendant god but denies revelation." Later in 18c. theist was contrasted with deist, as allowing the possibility of revelation.
theistic (adj.) Look up theistic at Dictionary.com
1780, from theist + -ic.
them Look up them at Dictionary.com
c.1200, from Old Norse þeim, dative of þeir "they" (see they). Replaced Old English cognate him, heom. Themselves is c.1500, a northern dialectal variant of Old English heom selfum (dative).
thematic (adj.) Look up thematic at Dictionary.com
1690s, from Greek thematikos, from thema (see theme). Related: Thematically.
theme (n.) Look up theme at Dictionary.com
c.1300, from Old French tesme (13c., with silent -s-), from Latin thema "a subject, thesis," from Greek thema "a proposition, subject, deposit," literally "something set down," from root of tithenai "put down, place," from PIE root *dhe- "to put, to do" (see factitious). Extension to music first recorded 1670s; theme song first attested 1929. Theme park is from 1960.
Themis Look up Themis at Dictionary.com
Greek goddess of law and justice, literally "custom, law, right;" related to theme "that which is placed" (see theme).
Themistocles Look up Themistocles at Dictionary.com
name of great Athenian political leader, from Greek Themistokles, literally "famed in law and right," from themis "custom, law, right" (see Themis) + -kles (see Damocles).
themselves Look up themselves at Dictionary.com
c.1500, standard from 1540s, replacing themself (cf. theirself). Themself returned late 20c. as some writers took to avoiding himself with gender-neutral someone, anyone, etc.
then Look up then at Dictionary.com
adverb of time, from Old English þanne, þænne, þonne, from Proto-Germanic *thana- (cf. Old Frisian thenne, Old Saxon thanna, Dutch dan, Old High German danne, German dann), from PIE demonstrative pronoun root *to- (see the). For further sense development, see than. Similar evolutions in other Germanic languages; Dutch uses dan in both senses, but German has dann (adv.) "then," denn (conj.) "than." Now and then "at various times" is attested from 1550s; earlier then and then (c.1200).
thence (adv.) Look up thence at Dictionary.com
late 13c., from Old English þanone, þanon "from that place" + adverbial genitive -es. Old English þanone/þanon is from West Germanic *thanana (cf. Old Saxon thanana, Old Norse þana, Old Frisian thana, Old High German danana, German von dannen), related obscurely to the root of then, and ultimately from PIE demonstrative base *to- (see the). Written with -c- to indicate a voiceless "s" sound. From thence is redundant.
thenceforth (adv.) Look up thenceforth at Dictionary.com
late 14c., from thence + forth.
thenceforward (adv.) Look up thenceforward at Dictionary.com
mid-15c., from thence + forward.
Theobald Look up Theobald at Dictionary.com
masc. proper name, from Medieval Latin Theobaldus, from Old High German Theudobald, from theuda "folk, people" + bald "bold." Form influenced in Medieval Latin by the many Greek-derived names beginning in Theo-.
theocentric (adj.) Look up theocentric at Dictionary.com
1886, from Greek theos "god" (see Thea) + -centric.
theocracy (n.) Look up theocracy at Dictionary.com
1620s, "sacerdotal government under divine inspiration" (as that of Israel before the rise of kings), from Greek theokratia "the rule of God" (Josephus), from theos "god" (see Thea) + kratos "a rule, regime, strength" (see -cracy). Meaning "priestly or religious body wielding political and civil power" is recorded from 1825.
theocrat (n.) Look up theocrat at Dictionary.com
1827, from Greek theos "god" (see Thea) + -crat, from aristocrat, etc. Related: Theocratic.
theodicy (n.) Look up theodicy at Dictionary.com
1799, from French théodicée, title of a work by Leibniz, from Greek theos "god" (see Thea) + dike "judgment, justice, usage, custom" (cognate with Latin dicere "to show, tell;" see diction).
theodolite (n.) Look up theodolite at Dictionary.com
1570s, of unknown origin (see OED for discussion).
Theodore Look up Theodore at Dictionary.com
masc. proper name, from Latin Theodorus, from Greek Theodoros, literally "gift of god," from theos "god" (see Thea) + doron "gift" (see date (n.1)).
Theodosia Look up Theodosia at Dictionary.com
fem. proper name, from Greek Theodosia, literally "gift of the gods," from theos "god" (see Thea) + dosis "gift."
Theodric Look up Theodric at Dictionary.com
masc. proper name, from Late Latin Theodricus, from Gothic, literally "ruler of the people," cf. Gothic þiuda "people" + *reiks "ruler." For spelling, see Theobald.
theogony (n.) Look up theogony at Dictionary.com
1610s, "the account of the birth or genealogy of the gods," from Greek theogonia "generation or birth of the gods," from theos "a god" (see Thea) + -gonia "a begetting."
theologian (n.) Look up theologian at Dictionary.com
late 15c., from Old French theologien (14c.); see theology. A petty or paltry theologist is a theologaster (1620s), coined in Medieval Latin by Martin Luther (1518).
theological (adj.) Look up theological at Dictionary.com
1520s, from Medieval Latin theologicalis, from Latin theologicus, from theologia (see theology). Earlier was theologic (late 15c.).
theologist (n.) Look up theologist at Dictionary.com
1630s, from Medieval Latin theologista, agent noun from theologizare, from Latin theologia (see theology).