Pro side (4)
I believe the answer is:
ayes
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pro side</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ayes that I've seen before include "Affirmative votes as in committee" , "Positive votes" , "Sounds of agreement" , "Votes of approval during 5 Down" , "The yes votes at committee meeting" .)