Attempt - to use a dagger (4)
I believe the answer is:
stab
This clue is a double definition.
'attempt to' is the first definition.
(I've seen this before)
'use a dagger' is the second definition.
(I've seen this in another clue)
(Other definitions for stab that I've seen before include "It could be the death of you" , "Pierce with something pointed" , "Go" , "effort" , "Wound with blade" .)