Make ineffective (7)
I believe the answer is:
nullify
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">make ineffective</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nullify that I've seen before include "Make of no effect" , "quash" , "Cancel, abolish" , "Declare invalid" , "Bring to naught" .)