- The definition of thy is your, or is the possessive form of thou.
An example of thy is a man making a reference to his friend's wife by saying thy wife.
thy definition by Webster's New World
Origin: Middle English thi, contr. ; from thin, thy: see thine
thy definition by American Heritage Dictionary
adjective The possessive form of thou1.
Origin: Middle English, variant of thin, thine, from Old English thīn; see tu- in Indo-European roots.