Cancelling out (10)
I believe the answer is:
nullifying
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cancelling out</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for nullifying that I've seen before include "Rendering void" , "Cancelling out" .)