Referee, adjudicator (7)
I believe the answer is:
arbiter
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">referee</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">adjudicator</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for arbiter that I've seen before include "One has the authority to settle disputes" , "Judge, final authority" , "Ref" , "Source of authority" , "Rarebit? (anag)" .)