Try to stop (5)
I believe the answer is:
deter
'try to stop' 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 "Put (someone) off" , "Try to prevent" , "Discourage (an activity)" , "'Discourage, dissuade (5)'" , "Daunt" .)