Insignificant detail (3)
I believe the answer is:
nit
'insignificant detail' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nit that I've seen before include "Egg of a louse (3)" , "Hair louse" , "Foolish person" , "Young louse" , "Egg of a head louse" .)