On behalf of (3)
I believe the answer is:
for
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">on behalf of</span>' is the definition.<br/ ><span class="explanation-format__explanation">(eg speaking on behalf of or for someone else)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for for that I've seen before include "Pro" , "In favour of; since" , "On the side of" , "and 16 and 20: Notwithstanding" , "Favouring" .)