An attempt to cause grievous bodily harm (4)
I believe the answer is:
stab
This clue could be a double definition.
'an attempt' is the first definition.
(to have a stab is to attempt something)
'grievous bodily harm' is the second definition.
'stab' can be an answer for 'harm' (thesaurus). I'm not certain of the 'grievous bodily' bit.
'to cause' acts as a link.
Can you help me to learn more?
(Other definitions for stab that I've seen before include "Pierce with pointed weapon" , "Wound with pointed weapon" , "Strike with knife" , "Jab" , "Wound with blade" .)