what is the mean thy

"Thy" is an English word that means "your" in the second person singular. English used to have a distinction between singular and plural in the second person, such that we had the following: Singular: thou, thee, thy Plural: ye, you, your Nowadays, we just have "you" and "your" in place of those six distinct words (which is why in nonstandard English, we have things like "y'all" or "youse" to distinguish 2nd-person plural from 2nd-person singular.

You/Your...