Act on (6)
I believe the answer is:
affect
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">act on</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 affect that I've seen before include "Arouse sadness or sympathy like tear-jerker" , "Act upon" , "Have repercussions on" , "Influence; make pretence of" , "impress" .)