Small bit of grit in your eye
I believe the answer is:
tiny
'small' is the definition.
(similar in meaning)
'bit of grit in your eye' is the wordplay.
'bit of' says the answer is hidden in the clue.
'TINY' is hidden in the letters of 'grit in your eye'.
(Other definitions for tiny that I've seen before include "Quite insignificant" , "Slight" , "Really small" , "Wee" , "Little" .)