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.
Archaic of, belonging to, made by, or done by thee
Origin of thyMiddle English thi, contr. from thin, thy: see thine
adjectiveThe possessive form of thou1
Used as a modifier before a noun.
Origin of thyMiddle English variant of thin thine from Old English thīn ; see tu- in Indo-European roots.
- (obsolete) because.