Kingpin (6)
I believe the answer is:
bigwig
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">kingpin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for bigwig that I've seen before include "Somebody" , "Important person (slang)" , "'Chief, top banana (6)'" , "Personage" , "Person of some importance" .)