Prevent, ward off (5)
I believe the answer is:
avert
This clue is a double definition.
'prevent' is the first definition.
(I know this)
'ward off' is the second definition.
(synonyms)
(Other definitions for avert that I've seen before include "Deflect away" , "Turn away or aside" , "Head off" , "Stop" , "Turn aside or ward off" .)