Definition of "thy"

thy¹

/ðaɪ/

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

thy²

/ðaɪ/

conjunction
1. (obsolete) Only used in for thy, for-thy, which is an alternative form of forthy (“because, therefore”)
  Quotations
  For-thy it round and hollow shaped was, Like to the world itselfe, and seem'd aworld of glass.
  1590, Edmund Spenser, The Faerie Queene
  Wallace knew well the Englishmen would flee, For thy he thrusted in the thickest to be, Hewing full fast on whomsoever he fought, Against his dint fine steel availed nought.
  1713, Robert Sanders, transl., The Life and Acts of Sir William Wallace
  For thy it bring: us nearer to the Godhead is nonsense, Daya, if not blasphemy.
  1791, Gotthold Ephraim Lessing, William TAYLOR (of Norwich.), Nathan the Wise. A dramatic poem, page 24