Mastermind (6)
I believe the answer is:
genius
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mastermind</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for genius that I've seen before include "Virtuoso" , "Person with extraordinary ability" , "Great mind" , "Exceptional intellectual power" , "Exceptionally intelligent person" .)