Pierce with a dagger (4)
I believe the answer is:
stab
'pierce with a dagger' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stab that I've seen before include "Rough guess; to knife" , "Wound with blade" , "Impale; attempt" , "Wound with pointed weapon" , "Sudden sharp feeling" .)