Subtle distinction or precision (6)
I believe the answer is:
nicety
I believe this clue is a double definition.
'subtle distinction' is the first definition.
(I've seen this before)
'precision' is the second definition.
(I've seen this before)
'or' acts as a link.
(Other definitions for nicety that I've seen before include "Fine distinction" , "Subtle point of distinction" , "Judge to a . . . . . . - with precision" , "Degree of precision" , "Small detail" .)