Guesstimate (4)
I believe the answer is:
stab
'guesstimate' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stab that I've seen before include "Attack with a knife" , "Sudden sharp pain" , "Thrust at and pierce" , "Attack with a dagger" , "Injure with knife" .)