What does thy?

Answer 1

Thy is an old-fashioned word for your. It is still used in some churches, for example, "Love Thy Neighbour!"

More specifically in Shakespearean/Elizabethan/King James era English, "thy" is the second person singular possessive pronoun. "Your" in contemporary English, of course, can mean either singular or plural, while in that era "your" would have been used exclusively for the plural. Similarly, the second person singular nominative is "thou" as opposed to the plural "ye." The second person singular objective is "thee" instead of the plural "you." First and third person pronouns remain unchanged.