Critically injure (4)
I believe the answer is:
maim
'critically injure' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for maim that I've seen before include "Wound, injure, harm" , "Disable, lame" , "Wound and permanently disfigure" , "Wound so that part of body is permanently damaged" , "Injure permanently" .)