Nouns:
* fly
* cry
* try
* sky
* spy
* dry
* fry
* buy
* guy
* ply
* sty
Verbs:
* cry
* try
* fly
* fry
* buy
* pry
* ply
* defy
Adjectives:
* dry
* sly
* shy
* wry
Pronouns:
* my
* thy
Interjections:
* hey
* oh my
Note: These are just a few examples. There are many other one-syllable words ending in "y" depending on the context and part of speech.