thou

英 [ðaʊ] 美 [ðaʊ]

1. [单数]主格thou;所有格 thy 或 thine;宾格thee;
2. [复数]主格 you 或 ye;所有格 your 或 yours; 宾格 you 或 ye.

thou （用作第二人称单数主格）你，汝

来自 you 的古体用法或诗意用法，来自古英语 thu,你，来自 Proto-Germanic*tu,你，来自 PIE*tu, 第二人称单数人称代词，你，词源同 thee,thine,thy.后由 you 所取代。

thou (pron.): 2nd nominative singular personal pronoun, Old English þu, from Proto-Germanic *thu (cognates: 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 (cognates: 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Superseded in Middle English by plural form you (from a different root), but retained in certain dialects (e.g. early Quakers).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.