From The Collaborative International Dictionary of English v.0.48 [gcide]: thou \thou\ ([th]ou), pron. [Sing.: nom. Thou; poss. Thy ([th][imac]) or Thine ([th][imac]n); obj. Thee ([th][=e]). Pl.: nom. You (y[=oo]); poss. Your (y[=oo]r) or Yours (y[=oo]rz); obj. You.] [OE. thou, [thorn]u, AS. [eth][=u], [eth]u; akin to OS. & OFries. thu, G., Dan. & Sw. du, Icel. [thorn][=u], Goth. [thorn]u, Russ. tui, Ir. & Gael. tu, W. ti, L. tu, Gr. sy`, Dor. ty`, Skr. tvam. [root]185. Cf. Thee, Thine, Te Deum.] The second personal pronoun, in the singular number, denoting the person addressed; thyself; the pronoun which is used in addressing persons in the solemn or poetical style. [1913 Webster] Art thou he that should come? --Matt. xi. 3. [1913 Webster] Note: "In Old English, generally, thou is the language of a lord to a servant, of an equal to an equal, and expresses also companionship, love, permission, defiance, scorn, threatening: whilst ye is the language of a servant to a lord, and of compliment, and further expresses honor, submission, or entreaty." --Skeat. [1913 Webster] Note: Thou is now sometimes used by the Friends, or Quakers, in familiar discourse, though most of them corruptly say thee instead of thou. [1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]: Thy \Thy\, pron. [OE. thi, shortened from thin. See Thine, Thou.] Of thee, or belonging to thee; the more common form of thine, possessive case of thou; -- used always attributively, and chiefly in the solemn or grave style, and in poetry. Thine is used in the predicate; as, the knife is thine. See Thine. [1913 Webster] Our father which art in heaven, Hallowed be thy name. Thy kingdom come. Thy will be done. --Matt. vi. 9,10. [1913 Webster] These are thy glorious works, Parent of good. --Milton. [1913 Webster]