Try to prevent (5)
I believe the answer is:
deter
'try to prevent' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for deter that I've seen before include "Frighten off; prevent" , "Put (someone) off" , "Discourage, put off" , "Try to prevent" , "Hinder, discourage" .)