One who doubts accepted opinions (7)
I believe the answer is:
sceptic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one who doubts accepted opinions</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 sceptic that I've seen before include "One is inclined to doubt accepted opinions" , "Disbeliever" , "Greek philosopher" , "One who doubts accepted opinions" , "Thomas for one" .)