Husband with gun injury (4)
I believe the answer is:
harm
'injury' is the definition.
(I know that injury can be written as harm)
'husband with gun' is the wordplay.
'husband' becomes 'h'.
'with' means one lot of letters go next to another.
'gun' becomes 'arm' (I've seen this in other clues).
'h'+'arm'='HARM'
(Other definitions for harm that I've seen before include "Trials, exams" , "See 13" , "Injure or damage" , "Hurt, injure" , "Hurt, maim" .)