A- (3) prefix meaning "not," from Gk a-, an- "not," from pie base *ne "not" (see un-)

Thaddeus --- masc. proper name, from L. Thaddaeus, from Gk. Thaddaios, from Talmudic Heb. Tadday.

Thai --- 1808, native name, from Tai, lit. "free." Thai stick "Asian marijuana cigarette" is attested by 1976.

thalamus --- 1753, "the receptacle of a flower," Mod.L., from L. thalamus "inner chamber," from Gk. thalamos "inner chamber, bedroom," related to thalame "den, lair," tholos "vault, vaulted building." Used since 1756 of a part of the forebrain where a nerve appears to originate.

Thalia --- fem. proper name, 1656, from Gk. Thaleia, lit. "luxuriant, blooming," from thallein "to bloom" (see thallium). Eighth of the Muses, presiding over comedy and idyllic poetry. Also one of the three Graces, patroness of festive meetings.

Thalidomide --- 1958, from "phthalimidoglutarimide," based on abbreviated form of naphthalene; a morning-sickness drug responsible for severe birth defects in Europe from 1956 to 1961, when it was withdrawn. It was never approved for use in America thanks to the efforts of Dr. Helen Brooke Taussig. Thalidomide baby is attested from 1962.

thallium --- rare metallic element, 1861, Mod.L., from Gk. thallos "young shoot, green branch," so called by its discoverer, Sir William Crookes (1832-1919), from the green line in its spectrum. Gk. thallos is related to thalia "abundance," thalos "scion, child," ult. from PIE base *dhal- "to bloom" (cf. O.Ir. duilesc, a type of algae).

Thames --- O.E. Temese, from L. Tamesis (51 B.C.E.), from Brit. Tamesa, an ancient Celtic river name perhaps meaning "the dark one."

Thammuz --- 1535, from Heb. tammuz, tenth month of the Jewish civil year, fourth of the sacred, covering parts of June and July; also the name of a Syrian deity equivalent to Phoenician Adon, whose festival began with the new moon of this month.

than --- O.E. þan, conjunctive particle used after a comparative adj. or adv., from þanne, þænne, þonne "then" (see then). Developed from the adverb then, and not distinguished from it in spelling until c.1700. The earliest use is in W.Gmc. comparative forms, i.e. bigger than (cf. Du. dan, Ger. denn), which suggests a semantic development from the demonstrative sense of then: A is bigger than B, evolving from A is bigger, then ("after that") B. Or the word may trace to O.E. þonne "when, when as," such as "When as" B is big, A is more (so).

thanatology --- 1842, "scientific study of death," from Gk. thanatos "death" (from PIE *dhwene- "to disappear, die," perhaps from root meaning "dark, cloudy") + -logia "treating of." Thanatism (1900) is the belief that at death the soul ceases to exist. Hence also Thanatos (1935), the "death instinct" in Freudian psychology. In 1970s, some undertakers made a bid to be called thanatologists.

thane --- O.E. ðegn "military follower," also "servant, attendant," from P.Gmc. *thegnas (cf. O.S. thegan "follower, warrior, boy," O.N. þegn "thane, freeman," O.H.G. thegan, Ger. Degen "thane, warrior, hero"), from PIE *tek-no- (cf. Skt. takman "descendant, child," Gk. teknon "child"), from base *tek- "to beget, give birth to" (cf. Gk. tekos "child, the young of animals," tokos "childbirth, offspring, produce of money, interest"). Also used in O.E. for "disciple of Christ." Specific sense of "man who ranks between an earl and a freeman" is c.1470. The modern spelling is from Scottish, where c.1220 it came to mean "chief of a clan, king's baron," and probably predominated in Eng. due to influence of "Macbeth;" normal orthographic changes from O.E. ðegn would have produced Mod.Eng. *thain. Some historians now use thegn to distinguish Anglo-Saxon thanes from Scottish thanes.

thank (v.) --- O.E. þancian "to give thanks," from P.Gmc. *thankojan (cf. O.S. thancon, O.N. þakka, Dan. takke, O.Fris. thankia, M.Du., Ger. danken "to thank"), from *thankoz "thought, gratitude," from PIE base *tong- "to think, feel." For sense evolution, cf. related O.E. noun þanc, þonc, originally "thought," but by c.1000 "good thoughts, gratitude." The whole group is from the same root as think (q.v.). In ironical use, "to blame," from 1560. Thankful is from O.E. þancfulle; thankless "likely to not be rewarded with thanks" is from c.1547. Thank you is attested from c.1400, short for I thank you. To thank (someone) for nothing is recorded from 1703.

thanksgiving --- 1533, "the giving of thanks," from thanks (n.) + giving. The noun thanks is attested from 1340, from the verb thank. In the specific sense of "public celebration acknowledging divine favors" thanksgiving dates from 1632 (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 1674.

that --- O.E. þæt, neuter sing. of the demonstrative pronoun and adj. (corresponding to masc. se, fem. seo), from P.Gmc. *that, from PIE *tod-, extended form of demonstrative pronomial base *to- (cf. Skt. ta-, Lith., O.C.S. to, Gk. to "the," L. talis "such"). Cf. the. Emerged c.1200 as a demonstrative adj. with the breakdown of the O.E. grammatical gender system, perhaps by infl. of Fr. and L., which had demonstrative adjectives (O.E. 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 c.1425.

thatch (v.) --- O.E. þeccan "to cover," related to þæc "roof, thatching material," from P.Gmc. *thakan (cf. O.S. thekkian, O.N. þekja, O.Fris. thekka, M.Du. decken, O.H.G. decchen, Ger. decken "to cover"), from PIE *(s)tog-/*(s)teg- "cover" (see stegosaurus). The noun is O.E. þæc "roof, thatch," from the verb (cf. O.N. þak, O.Fris. thek, M.Du. dak "roof," O.H.G. dah, Ger. Dach "roof").

thaumaturge --- 1621 (implied in thaumaturgical), from Mod.L., from Gk. thaumatourgos "wonder-working, conjurer," from thauma (gen. thaumatos) "wonder, wonderous thing," prop. "a thing to look at" (from root of theater, q.v.) + ergon "work" (see urge (v.)).

thaw (v.) --- O.E. þawian, from P.Gmc. *thawojanan (cf. O.N. þeyja, M.L.G. doien, Du. dooien, O.H.G. douwen, Ger. tauen "to thaw"), from PIE base *ta- "to melt, dissolve" (cf. Skt. toyam "water," Ossetic thayun "to thaw," Welsh tawadd "molten," Doric Gk. takein "to melt, waste, be consumed," O.Ir. tam "pestilence," L. tabes "a melting, wasting away, putrefaction," O.C.S. tajati "to melt"). The noun is c.1400, from the verb. Fig. sense of "relaxation of political harshness or hostility" is recorded from 1950, an image from the Cold War.

the --- late O.E. þe, nom. masc. form of the demonstrative pronoun and adj. After c.950, it replaced earlier se (masc.), seo (fem.), þæt (neut.), and probably represents se altered by the þ- form which was used in all the masc. oblique cases (see below). O.E. se is from PIE base *so- "this, that" (cf. Skt. sa, Avestan ha, Gk. ho, he "the," Ir., Gael. so "this"). For the þ- forms, see that. The s- forms were entirely superseded in Eng. by c.1250, excepting dial. survival slightly longer in Kent. O.E. 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). Adv. use in the more the merrier, the sooner the better, etc. is a relic of O.E. þy, originally the instrumentive case of the neuter demonstrative þæt (see that).

Thea --- fem. proper name, from Gk. thea "goddess," fem. equivalent of theos "god," from PIE base *dhes-, root of words applied to various religious concepts, e.g. L. feriae "holidays," festus "festive," fanum "temple."

theater --- c.1374, "open air place in ancient times for viewing spectacles," from O.Fr. theatre (12c.), from L. theatrum, from Gk. theatron "theater," lit. "place for viewing," from theasthai "to behold" (cf. thea "a view," theates "spectator") + -tron, suffix denoting place. Meaning "building where plays are shown" (1577) was transferred to that of "plays, writing, production, the stage" (1668). Spelling with -re prevailed in Britain after c.1700, but Amer.Eng. retained or revived the older spelling in -er. Generic sense of "place of action" is from 1581; especially "region where war is being fought" (1914). Theatrical "pertaining to the theater" is recorded from 1558; in the sense of "stagy, histrionic" it is attested from 1709.

Thebaid --- 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- --- prefix used in botany and zoology, from combining form of Gk. theke "case, receptacle," from base of tithenai "to put, place" (see theme).

thee --- O.E. þe (accusative and dative singular of þu "thou"), from P.Gmc. *theke (cf. O.Fris. thi, M.Du. di, O.H.G. dih, Ger. dich, O.N. þik, Norw. deg, Goth. þuk), from PIE *tege-. A brief history of the second person pronoun in Eng. 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).

theft --- O.E. þeofð (W.Saxon þiefð), from P.Gmc. *theubitho (cf. O.Fris. thiufthe, O.N. þyfð), from *theubaz "thief" (see thief) + suffix -itha (cognate with L. -itatem).

thegn --- military tenant of an Anglo-Saxon king, a modern revival first attested 1848; see thane.

their --- c.1200, from O.N. þierra, gen. of þeir "they" (see they). Replaced O.E. hiera. Use with singular objects, scorned by grammarians, is attested from c.1300. Theirs (c.1300) is a double possessive. Alternate form theirn (1836) is attested in Midlands and southern dialect in U.K. and the Ozarks region of the U.S.

theist --- 1662, from Gk. 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. Theism "belief in a deity" is recorded from 1678; meaning "belief in one god" (as opposed to polytheism) is recorded from 1711. Theistic is attested from 1780.

them --- c.1200, from O.N. þeim, dat. of þeir "they" (see they). Replaced O.E. cognate him, heom. Themselves is c.1500, a northern dial. variant of O.E. heom selfum (dative).

theme --- c.1300, from O.Fr. tesme (13c., with silent -s-), from L. thema "a subject, thesis," from Gk. thema "a proposition, subject, deposit," lit. "something set down," from root of tithenai "put down, place," from PIE base *dhe- "to put, to do" (see factitious). Extension to music first recorded 1674; theme song first attested 1929. Theme park is from 1960.

Themis --- 1656, from Gk. Themis, goddess of law and justice, lit. "custom, law, right;" related to theme "that which is placed" (see theme).

Themistocles --- name of great Athenian political leader, from Gk. Themistokles, lit. "famed in law and right," from themis "custom, law, right" (see Themis) + -kles (see Damocles).

then --- adverb of time, from O.E. þanne, þænne, þonne, from P.Gmc. *thana- (cf. O.Fris. thenne, O.S. thanna, Du. dan, O.H.G. danne, Ger. dann), from PIE demonstrative pronoun root *to- (see the). For further sense development, see than. Similar evolutions in other Gmc. languages; Du. uses dan in both senses, but Ger. has dann (adv.) "then," denn (conj.) "than." Now and then "at various times" is attested from c.1550; earlier then and then (c.1205).

thence --- c.1290, from O.E. þanone, þanon "from that place" + adverbial genitive -es. O.E. þanone, þanon is from W.Gmc. *thanana (cf. O.S. thanana, O.N. þana, O.Fris. thana, O.H.G. danana, Ger. von dannen), related obscurely to the root of then, and ult. from PIE demonstrative base *to- (see the). Written with -c- to indicate a voiceless "s" sound. From thence is redundant. Thenceforth is c.1374; thenceforward attested from 1457.

Theobald --- masc. proper name, from M.L. Theobaldus, from O.H.G. Theudobald, from theuda "folk, people" + bald "bold." Form infl. in M.L. by the many Gk-derived names beginning in Theo-.

theocracy --- 1622, "sacerdotal government under divine inspiration" (as that of Israel before the rise of kings), from Gk. theokratia "the rule of God" (Josephus), from theos "god" (of unknown origin, perhaps a non-I.E. word) + kratos "a rule, regime, strength" (see -cracy). Meaning "priestly or religious body wielding political and civil power" is recorded from 1825.

Theodore --- masc. proper name, from L. Theodorus, from Gk. Theodoros, lit. "gift of god," from theos "god" (see Thea) + doron "gift."

Theodosia --- fem. proper name, from Gk. Theodosia, lit. "gift of the gods," from theos "god" (see Thea) + dosis "gift."

Theodric --- masc. proper name, from L.L. Theodricus, from Goth., lit. "ruler of the people," cf. Goth. þiuda "people" + *reiks "ruler." For spelling, see Theobald.

theogony --- 1612, "the account of the birth or genealogy of the gods," from Gk. theogonia "generation or birth of the gods," from theos "a god" (see Thea) + -gonia "a begetting."

theology --- 1362, from O.Fr. theologie "philosophical treatment of Christian doctrine" (14c.), from L. theologia, from Gk. theologia "an account of the gods," from theologos "one discoursing on the gods," from theos "god" (see Thea) + -logos "treating of."

Theophilus --- masc. proper name, from Gk., lit. "loved by the gods," from theos "god" (see Thea) + philos "loved, beloved."

theorem --- 1551, from M.Fr. théorème, from L.L. theorema, from Gk. theorema "spectacle, speculation," in Euclid "proposition to be proved," from theorein "to consider" (see theory).

theoretical --- 1616, from L.L. theoreticus "of or pertaining to theory" (c.397), from Gk. theoretikos "contemplative, pertaining to theory" (by Aristotle contrasted to praktikos), from theoretos "that may be seen or considered," from theorein "to consider, look at" (see theory).

theory --- 1592, "conception, mental scheme," from L.L. theoria (Jerome), from Gk. theoria "contemplation, speculation, a looking at, things looked at," from theorein "to consider, speculate, look at," from theoros "spectator," from thea "a view" + horan "to see." Sense of "principles or methods of a science or art (rather than its practice)" is first recorded 1613. That of "an explanation based on observation and reasoning" is from 1638. The verb theorize is recorded from 1638.

theosophy --- 1642 (implied in theosophical), "knowledge about God and nature obtained through mystical study," from M.L. theosophia (c.880), from Late Gk. theosophia (c.500, Pseudo-Dionysus) "wisdom concerning God or things divine," from Gk. theosophos "one wise about God," from theos "god" (see Thea) + sophos "wise, learned." Taken as the name of a modern philosophical system (sometimes called Esoteric Buddhism), founded in New York 1875 as "Theosophical Society" by Madame Blavatsky and others, which combines teachings of Hinduism and Buddhism.

therapeutic --- of or pertaining to the healing of disease, 1646, probably shortened from therapeutical (1605), from Mod.L. therapeuticus "curing, healing," from Gk. therapeutikos, from therapeutes "one ministering," from therapeutein "to cure, treat," of unknown origin, related to therapon (gen. therapontos) "attendant." Therapeutic was used from 1541 as a noun meaning "the branch of medicine concerned with treatment of disease."

therapy --- 1846, "medical treatment of disease," from Mod.L. therapia, from Gk. therapeia "curing, healing," from therapeuein "to cure, treat." Therapist formed 1886; earlier therapeutist (1816), especially of psychotherapy practitioners from c.1930s.

there --- O.E. þær "in or at that place," from P.Gmc. *thær (cf. O.S. thar, O.Fris. ther, M.L.G. dar, M.Du. daer, Du. daar, O.H.G. dar, Ger. da, Goth. þar, O.N. þar), from PIE *tar- "there" (cf. Skt. tar-hi "then"), from base *to- (see the) + adverbial suffix -r. Interjectional use is recorded from 1535. To have been there "had previous experience of some activity" is recorded from 1877.

thereabouts --- c.1400, from O.E. þærabutan + adv. gen. -es; see there + about.

thereafter --- O.E. þær æfter; see there + after. Cf. Du. daarachter, Swed. derefter.

thereby --- O.E. þærbig "by means of or because of that;" see there + by. Cf. Ger. dabei, Du. daarbij.

therefore --- O.E. þærfore; from there + fore, O.E. and M.E. collateral form of for. Since c.1800, therefor has been used in sense of "for that, by reason of that;" and therefore in sense of "in consequence of that."

therein --- O.E. þærin; see there + in.

thereof --- O.E. þær of; see there + of.

thereon --- O.E. þæron; see there + on.

Theresa --- fem. proper name, from Fr. Thérèse, from L. Therasia, apparently from Gk. Therasia, name of two volcanic islands, one near Sicily, one near Crete.

thereunder --- O.E. þærunder; see there + under.

thereupon --- c.1175, þer uppon; see there + upon.

therewith --- O.E. þær wiþ; see there + with.

thermal (adj.) --- 1756, "having to do with hot springs," from Fr. thermal (Buffon), from Gk. therme "heat," from PIE *ghwerm-/*ghworm- "warm" (cf. L. fornax "an oven, kiln," formus "warm," O.E. wearm; see warm). Sense of "having to do with heat" is first recorded 1837. The noun meaning "rising current of relatively warm air" is recorded from 1933.

thermo- --- comb. form meaning "hot, heat," used in scientific and technical words, from Gk. thermos "hot," therme "heat" (see thermal).

thermodynamics --- theory of relationship between heat and mechanical energy, 1854, from adj. thermodynamic (1849), from thermo- + dynamic.

thermometer --- 1633, from Fr. thermomètre (1624), coined by Jesuit Father Leuréchon from Gk. thermos "hot" (see thermal) + metron "measure" (see meter (2)). An earlier, Latinate form was thermoscopium (1617). The earliest such device was Galileo's air-thermometer, invented c.1597.

thermonuclear --- 1938 with ref. to stars, 1953 of weapons (technically only to describe the hydrogen bomb), from thermo- + nuclear.

Thermos --- trademark registered in Britain 1907, invented by Sir James Dewar (patented 1904 but not named then), from Gk. thermos "hot" (see thermal). Dewar built the first one in 1892, but it was first manufactured commercially in Germany in 1904, when two glass blowers formed Thermos GmbH. Supposedly the company sponsored a contest to name the thing, and a Munich resident won with a submission of Thermos.

thermostat --- 1831, from thermo- + -stat, from Gk. statos "a standing," from PIE base *sta- "to stand" (see stet).

thero- --- comb. form meaning "beast," from Gk. comb. form of ther "wild beast," from PIE *ghwer- "wild beast" (cf. L. ferus "wild," ferox "fierce;" see fierce).

thesaurus --- 1823, "treasury, storehouse," from L. thesaurus "treasury, treasure," from Gk. thesauros "a treasure, treasury, storehouse, chest," from root of tithenai "to put, to place." The meaning "encyclopedia filled with information" is from 1840, but existed earlier as thesaurarie (1592), used as a title by early dictionary compilers. Meaning "collection of words arranged according to sense" is first attested 1852 in Roget's title. Thesaur is attested in M.E. with the meaning "treasure" (15c.-16c.).

these --- O.E. þæs, variant of þas, nom. and acc. pl. of þes, þeos, þis "this" (see this).

thesis --- 1398, "unaccented syllable or note," from L. thesis "unaccented syllable in poetry," later "stressed part of a metrical foot," from Gk. thesis "a proposition," also "downbeat" (in music), originally "a setting down or placing," from root of tithenai "to place, put, set," from PIE base *dhe- "to put, to do" (see factitious). Sense in logic of "a proposition, statement to be proved" is first recorded 1579; that of "dissertation written by a candidate for a university degree" is from 1653.

thespian (adj.) --- 1675, "of or pertaining to tragedy or dramatic acting," from Gk. Thespis, poet of 6c. B.C.E., the traditional father of Gk. tragedy. The names is lit. "inspired by the gods." The noun meaning "an actor" is attested from 1827, from the adj.; short form thesp is attested from 1962.

Thetis --- 1422, name of a sea nymph or Nereid, mother of Achiles. Sometimes in poetry, "the sea personified."

thews --- O.E. þeawes "customs, manners, personal qualities," pl. of þeaw "habit, custom," from P.Gmc. *thawaz (cf. O.S. thau "usage, custom, habit," O.H.G. thau "discipline"); no certain cognates outside W.Gmc. Meaning "bodily powers or parts indicating strength, good physique" is attested from 1566, from notion of "good qualities." Acquired a sense of "muscular development" when it was revived by Scott (1818).

they --- c.1200, from O.N. þeir, originally masculine plural demonstrative pronoun, from P.Gmc. *thai, nom. pl. pronoun, from PIE *to- (see that). Gradually replaced O.E. hi, hie, plurals of he, heo, hit (see he, she, it) by c.1400. Colloquial use for "anonymous people in authority" is attested from 1886.

thiamin --- vitamin B1, 1937, coined by Dr. R.R. Williams from thio-, from comb. form of Gk. theion "sulfur" + amine.

thick (adj.) --- O.E. þicce "not thin, dense," from P.Gmc. *theku-, *thekwia- (cf. O.S. thikki, O.H.G. dicchi, Ger. dick, O.N. þykkr, O.Fris. thikke), from PIE *tegu- "thick" (cf. Gaelic tiugh). Secondary O.E. sense of "close together" is preserved in thickset and proverbial phrase thick as thieves (1833). Meaning "stupid" is first recorded 1597. Phrase thick and thin is in Chaucer (c.1386); thick-skinned is attested from 1545; in fig. sense from 1602. Verb thicken is first recorded c.1425 (trans.), 1598 (intrans.); an earlier verb was O.E. þiccian. To be in the thick of some action, etc., "to be at the most intense moment" is from 1681, from a M.E. noun sense.

thickening --- substance used to thicken something, 1839, from thicken (see thick).

thicket --- late O.E. þiccet, from þicce (see thick) + denominative suffix -et.

thickset --- c.1366, thikke sette "with parts or things set close together" (of grass on a sward, etc.), from thick + set (v.). Meaning "Stocky, strong and square-built" is recorded from 1724.

thief --- O.E. þeof, from P.Gmc. *theubaz (cf. O.Fris. thiaf, O.S. thiof, M.Du. dief, O.H.G. diob, Ger. dieb, O.N. þiofr, Goth. þiufs), probably from PIE *teup- (cf. Lith. tupeti "to crouch down").

thieve --- O.E. þeofian, from þeof (see thief). Rare in O.E., not common until 17c. Thievish "of or pertaining to thieves" is recorded from c.1450; meaning "inclined to steal" is from 1538. Thieving first attested 1530. Thievery is from 1568.

thigh --- O.E. þeoh, þeh, from P.Gmc. *theukhom (cf. O.Fris. thiach, O.Du. thio, Du. dij, O.N. þjo, O.H.G. dioh), from PIE *teuk- from base *teu- "to swell" (cf. Lith. taukas, O.C.S. tuku, Rus. tuku "fat of animals;" Lith. tukti "to become fat;" Gk. tylos "callus, lump," tymbos "burial mound, grave, tomb;" O.Ir. ton "rump;" L. tumere "to swell," tumulus "raised heap of earth," tumor "a swelling;" M.Ir. tomm "a small hill," Welsh tom "mound"). Thus thigh is lit. "the thick or fat part of the leg."

thilk --- the very thing, c.1225, from þe "the" + ilce "same" (see ilk).

thimble --- O.E. þymel "sheath or covering for the thumb," from thuma (see thumb) + -el, suffix used in forming names of instruments (cf. handle). Excrescent -b- began c.1440 (cf. humble, nimble). Originally of leather, metal ones came into use 17c. Thimblerig, con game played with three thimbles and a pea or button, is attested from 1825 by this name, though references to thimble cheats, probably the same swindle, date back to 1716.

thin --- O.E. þynne "narrow, lean, scanty," from P.Gmc. *thunnuz, *thunw- (cf. W.Fris. ten, M.L.G. dunne, Du. dun, O.H.G. dunni, Ger. dünn, O.N. þunnr), from PIE *tnus-, *tnwi-, from weak grade of base *ten- "stretch" (cf. L. tenuis "thin, slender;" see tenet).

thine --- O.E. þin, possessive pronoun (originally gen. of þu "thou"), from P.Gmc. *thinaz (cf. O.Fris., O.S. thin, M.Du. dijn, O.H.G. din, Ger. dein, O.N. þin), from PIE *t(w)eino-, suffixed form of second pers. sing. pronomial base *tu-. A brief history of the second person pronoun in Eng. can be found here; see also thou.