Countermand (8)
I believe the answer is:
overrule
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">countermand</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 overrule that I've seen before include "Veto" , "This is not OK" , "Don't allow" , "Reverse another's decision" , "Reject (decision) using superior authority" .)