THY

Etymology 1

Determiner

thy

(archaic, dialectal, literary) Possessive form of thou: that which belongs to thee; which belongs to you (singular).

Etymology 2

Conjunction

thy

(obsolete) Only used in for thy, for-thy, which is an alternative form of forthy (“because, therefore”)

Determiner

Thy

Honorific alternative letter-case form of thy, sometimes used when referring to God or another important figure who is understood from context.

Source: Wiktionary

Thy, pron. Etym: [OE. thi, shortened from thin. See Thine, Thou.]

Definition: 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.

Source: Webster’s Unabridged Dictionary 1913 Edition