Suffix -Y is a vowel suffix and changes the base word to name a “kind” or “type”, as in “dust” to “dusty”.

Suffix /ē/, Suffix /ē/, Suffix /ē/, dusty

When Y is at the end of a word, it is not always acting like a suffix.  When at the end of a one-syllable word, as in “spy”, it is not a suffix. And, at the end of some words, it may be part of a vowel team, as in “toy” or “play”.