- 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.
Origin: Middle English thi, contr. from thin, thy: see thine
Used by arrangement with John Wiley & Sons, Inc.
adjective The possessive form of thou1.
Origin: Middle English, variant of thin, thine, from Old English thīn; see tu- in Indo-European roots.