Leader, ruler (5)
I believe the answer is:
chief
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">leader</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(chief is a kind of leader)</span><br/ ><br/ >'<span class="explanation-format__original">ruler</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for chief that I've seen before include "Gaffer" , "Person in charge, head" , "Key" , "Boss" , "Tribal head" .)