Top boss (7)
I believe the answer is:
supremo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">top boss</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 supremo that I've seen before include "Leader with unlimited powers" , "Overall head" , "Person invested with great authority" , "Person in overall charge, top banana" , "Top commander" .)