Treaty partner (4)
I believe the answer is:
ally
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">treaty partner</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ally that I've seen before include "Friend and colleague" , "State formally cooperating with another" , "Confederate; supporter" , "Join - friend" , "Join forces with" .)