Over-fastidious person (6)
I believe the answer is:
purist
'over-fastidious person' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for purist that I've seen before include "Stir up (anag) - pedant" , "scrupulous" , "Over-fastidious person" , "Stickler for correctness, especially in language" , "Fastidious person" .)