Proposer (5)
I believe the answer is:
mover
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">proposer</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mover that I've seen before include "Instigator, organiser" , "One who is in motion - may also be a shaker" , "someone who brings forward proposal" , "Formal proposer" , "Someone who proposes a motion for debate" .)