A form of the possessive case of the pronoun thou, now superseded in common discourse by your, the possessive of you, but maintaining a place in solemn discourse, in poetry, and in the usual language of the Friends, or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
Thine is an old-fashioned, poetic, or religious word for `yours' when you are talking to only one person. I am Thine, O Lord, I have heard Thy voice. Used instead of thy before an initial vowel or h: "The presidential candidates are practicing the first rule of warfare: know thine enemy" (Eleanor Clift)