Webster's Revised Unabridged Dictionary · 1913

Thy

Thy , pronoun

[Old English 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