A bit of a nasty eye (4)

I believe the answer is:

stye

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for stye that I've seen before include "Eye problem" , "Inflammation around the eye" , "dump" , "Observer's problem" , "Red eye" .)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.