Nitpickers split them (5)
I believe the answer is:
hairs
'nitpickers split them' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hairs that I've seen before include "Skin growths" , "Fur filaments" , "Threadlike growths" , "See 3" , "eg Bristles" .)