Be courageous enough to try (4)
I believe the answer is:
dare
'be courageous enough to try' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for dare that I've seen before include "Take the risk, face the danger" , "Challenge of courage" , "Be brave enough" , "Challenge to do something foolhardy" , "Challenge to do something dangerous" .)