Wrong hospital wing (4)
I believe the answer is:
harm
'wrong' is the definition.
(thesaurus)
'hospital wing' is the wordplay.
'hospital' becomes 'h'.
'wing' becomes 'arm' (both can mean a side).
'h'+'arm'='HARM'
(Other definitions for harm that I've seen before include "Hurt, maim" , "Hurt, injure" , "Injure, injury" , "Injure or damage" , "Damage, hurt" .)