Associate, confederate (4)
I believe the answer is:
ally
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">associate</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(ally is a kind of associate)</span><br/ ><br/ >'<span class="explanation-format__original">confederate</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for ally that I've seen before include "Colleague, confederate" , "Supporter in a conflict" , "Friend and colleague" , "State formally cooperating with another" , "Friend, partner" .)