Thy definitions

Webster's 1828 Dictionary

THY, a. [contracted from thine, or from some other derivative of thou. It is probable that the pronoun was originally thig, thug or thuk, and the adjective thigen. See Thou.]
Thy is the adjective of thou, or a pronominal adjective, signifying of thee, or belonging to thee, like tuus in Latin. It is used in the solemn and grave style.
These are thy works, parent of good.
Thyine wood, a precious wood, mentioned Revelation 18.

Merriam Webster's

adjective Etymology: Middle English thin, thy, from Old English th?n, genitive of th? thou — more at thou Date: 12th century archaic of or relating to thee or thyself especially as possessor or agent or as object of an action — used especially in ecclesiastical or literary language and sometimes by Friends especially among themselves

Oxford Reference Dictionary

poss.pron. (attrib.) (also thine before a vowel) of or belonging to thee: now replaced by your except in some formal, liturgical, dialect, and poetic uses. Etymology: ME thi, reduced f. thin THINE

Webster's 1913 Dictionary

Thou Thou, pron. [Sing.: nom. Thou; poss. Thyor Thine; obj. Thee. Pl.: nom. You; poss. Youror Yours; 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.

Webster's 1913 Dictionary

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. Our father which art in heaven, Hallowed be thy name. Thy kingdom come. Thy will be done. --Matt. vi. 9,10. These are thy glorious works, Parent of good. --Milton.

Collin's Cobuild Dictionary

Thy is an old-fashioned, poetic, or religious word for 'your' when you are talking to one person. Honor thy father and thy mother. DET