Nit-picking (8)
I believe the answer is:
pedantic
'nit-picking' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pedantic that I've seen before include "Overly concerned with minor details" , "Excessively scrupulous" , "Abstruse" , "Fussy about correctness" , "Academic or didactic" .)