Prevent, ward off (5)
I believe the answer is:
avert
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">prevent</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ >'<span class="explanation-format__original">ward off</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for avert that I've seen before include "Deflect away" , "Turn away or aside" , "Head off" , "Stop" , "Turn aside or ward off" .)