A bit of a nasty eyesore (4)
I believe the answer is:
stye
'a bit' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'of a nasty eyesore' is the wordplay.
'of' says the answer is hidden in the clue.
'STYE' is hidden in the letters of 'nasty eyesore'.
Can you help me to learn more?
(Other definitions for stye that I've seen before include "Eye problem" , "Tamworth residence" , "Eye sore" , "makes viewer sore" , "Infection on the edge of the eye" .)