2nd nominative singular personal pronoun, Old English þu, from Proto-Germanic *thu (source also of Old Frisian thu, Middle Dutch and Middle Low German du, Old High German and German du, Old Norse þu, Gothic þu), from PIE *tu-, second person singular pronoun (source also of Latin tu, Irish tu, Welsh ti, Greek su, Lithuanian tu, Old Church Slavonic ty, Sanskrit twa-m).
Superseded in Middle English by plural form you (from a different root), but retained in certain dialects (e.g. early Quakers). The plural at first was used in addressing superior individuals, later also (to err on the side of propriety) strangers, and ultimately all equals. By c. 1450 the use of thou to address inferiors gave it a tinge of insult unless addressed by parents to children, or intimates to one another. Hence the verb meaning "to use 'thou' to a person" (mid-15c.).
Avaunt, caitiff, dost thou thou me! I am come of good kin, I tell thee!
["Hickscorner," c. 1530]
A brief history of the second person pronoun in English can be found here.
colloquial for "the French language," 1754, from French parlez-vous (français?) "do you speak (French?)" From parlez, second person plural of parler "to speak" (see parley (n.)) + vous, from Latin vos, plural of tu "thou" (see thou). Also used as a verb, "to speak French." It got another boost in U.S. after World War I, along with other mangled French terms brought home by the doughboys, such as san fairy ann, a jocular expression of indifference, representing French ça ne fait rien "it does not matter."
Old English ge, nominative plural of 2nd person pronoun þu (see thou); cognate with Old Frisian ji, Old Saxon gi, Middle Dutch ghi, Dutch gij. Cognate with Lithuanian jūs, Sanskrit yuyam, Avestan yuzem, Greek hymeis.
Altered, by influence of we, from an earlier form that was similar to Gothic jus "you (plural)" (see you). The -r- in Old Norse er, German ihr probably is likewise from influence of their respective 1st person plural pronouns (Old Norse ver, German wir).
Pronunciation of you and the nominative form ye gradually merged from 14c.; the distinction between them passed out of general usage by 1600. Widespread use of French in England after 12c. gave English you the same association as French vous, and it began to drive out singular nominative thou, originally as a sign of respect (similar to the "royal we") when addressing superiors, then equals and strangers, and ultimately (by c. 1575) becoming the general form of address. Through 13c. English also retained a dual pronoun ink "you two; your two selves; each other."
Old English þe (accusative and dative singular of þu "thou"), from Proto-Germanic *theke (source also of Old Frisian thi, Middle Dutch di, Old High German dih, German dich, Old Norse þik, Norwegian deg, Gothic þuk), from PIE *tege-, accusative of root *tu-, second person singular pronoun (see thou). The verb meaning "to use the pronoun 'thee' to someone" is recorded from 1662, in connection with the rise of Quakerism.
In Middle English, people began to use plural forms in all cases, at first as a sign of respect to superiors, then as a courtesy to equals. By the 1600s, the singular forms had come to represent familiarity and lack of status, and fell from use except in the case of a few dialects, notably in the north of England. People in Lancashire north of the Rossendale Forest and Yorkshire formerly were noted for use of the singular second person pronouns tha (nom.) and thee (acc.). For religious reasons (Christian equality of persons, but also justified as grammatically correct), the Quakers also retained the familiar forms.
Thou and Thee was a sore cut to proud flesh and them that sought self-honour, who, though they would say it to God and Christ, could not endure to have it said to themselves. So that we were often beaten and abused, and sometimes in danger of our lives, for using those words to some proud men, who would say, "What! you ill-bred clown, do you Thou me?" as though Christian breeding consisted in saying You to one; which is contrary to all their grammar and teaching books, by which they instructed their youth. [George Fox's journal, 1661]
While the Quakers originally adopted "thee" and "thou" on account of their grammatical correctness, they soon fell into the careless habit of using "thee," the objective, instead of "thou," the nominative. Common illustrations are: "How does thee do?" or "Will thee," etc. [George Fox Tucker, "A Quaker Home," Boston, 1891]
"because, inasmuch as, since," used as such from early 16c., originally the present-participle of see (v.).
Then answered the iewes and sayde unto him: what token shewest thou unto us, seynge that thou dost these thynges? [Tyndale, 1526, John ii.18; where Wyclif, 1382, has What token schewist thou to vs, that thou doist these thingis?]
c. 1500, kind of small bird that has its tail in continuous motion (late 12c. as a surname), earlier wagstart (mid-15c.), from wag (v.) + tail (n.). From 18c. as "a harlot," but this sense seems to be implied much earlier:
If therefore thou make not thy mistress a goldfinch, thou mayst chance to find her a wagtaile. [Lyly, "Midas," 1592]
1530s, "withdraw, withhold, take away, deduct," a back-formation from subtraction (q.v.), or else from Latin subtractus, past participle of subtrahere "take away, draw off." Related: Subtracted; subtracting. Mathematical calculation sense is from 1550s. Earlier verb form was subtraien (early 15c. in the mathematical sense), which is directly from the Latin verb.
Here he teches þe Craft how þou schalt know, whan þou hast subtrayd, wheþer þou hast wel ydo or no. ["Craft of Numbering," c. 1425]