Cancel, revoke (5)
I believe the answer is:
annul
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cancel</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(annulling is a kind of cancelling)</span><br/ ><br/ >'<span class="explanation-format__original">revoke</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for annul that I've seen before include "Repeal, rescind" , "Cancel officially" , "Scrap" , "Declare (a law) invalid" , "Countermand" .)