What does the prefix y mean?

The prefix "y-" is not a standard prefix in English. It's possible you're thinking of a different prefix, or the word you're looking at has a different origin.

Could you please provide more context? For example:

* What word are you looking at?

* What is the word's meaning?

* What language is the word from?

Knowing this information will help me understand what you're asking and give you a more accurate answer.