Fine distinction (6)
'fine distinction' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nicety that I've seen before include "Subtle difference" , "Nuance - icy net (anag)" , "Judge to a . . . . . . - with precision" , "Exactitude" , "Matter of delicate adjustment" .)
(Other definitions for nuance that I've seen before include "Subtle difference of meaning" , "Delicate shade of difference" , "Subtle shade of difference" , "Slight difference in meaning etc" , "Subtle distinction or variation" .)