Subtle point or refinement (6)
I believe the answer is:
nicety
This clue is a double definition.
'subtle point' is the first definition.
(I've seen this before)
'refinement' is the second definition.
(synonyms)
(Other definitions for nicety that I've seen before include "Fine distinction" , "Fastidiousness" , "Matter of delicate adjustment" , "shade?" , "Subtle point of distinction" .)