Agent of change (8)
I believe the answer is:
catalyst
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">agent of change</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 catalyst that I've seen before include "It initiates a chemical reaction without itself being affected" , "Something that aids change" , "Cause of change, itself unchanged" , "Chemical influencing change" , "Person or thing that precipitates change" .)