What is "thine"

Thine \Thine\ ([th][imac]n), pron. & a. [OE. thin, AS. [eth][=i]n, originally gen. of [eth]u, [eth][=u], thou; akin to G. dein thine, Icel. [thorn]inn, possessive pron., [thorn][=i]n, gen. of [thorn][=u] thou, Goth. [thorn]eins, possessive pron., [thorn]eina, gen. of [thorn]u thou. See Thou, and cf. Thy.] A form of the possessive case of the pronoun thou, now superseded in common discourse by your, the possessive of you, but maintaining a place in solemn discourse, in poetry, and in the usual language of the Friends, or Quakers.

Note: In the old style, thine was commonly shortened to thi (thy) when used attributively before words beginning with a consonant; now, thy is used also before vowels. Thine is often used absolutely, the thing possessed being understood.

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.

Art thou he that should come?
--Matt. xi. 3.

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.

Note: Thou is now sometimes used by the Friends, or Quakers, in familiar discourse, though most of them corruptly say thee instead of thou.

Old English þin, possessive pronoun (originally genitive of þu "thou"), from Proto-Germanic *thinaz (cognates: Old Frisian, Old Saxon thin, Middle Dutch dijn, Old High German din, German dein, Old Norse þin), from PIE *t(w)eino-, suffixed form of second person singular pronomial base *tu-. A brief history of the second person pronoun in English can be found here; see also thou.

det. (context archaic English) Singular second person prevocalic possessive determiner (preconsonantal form: '''thy'''). pron. (context archaic English) Singular second person possessive pronoun.