Over-fastidious person (6)
I believe the answer is:
purist
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">over-fastidious person</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)