Shock answer Northerner returned (5)
I believe the answer is:
appal
'shock' is the definition.
('appal' can be a synonym of 'shock')
'answer northerner returned' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'northerner' becomes 'lapp' (I have seen 'Far northerner' mean 'lapp' so perhaps 'northerner' could also mean 'lapp'**).
'returned' shows that the letters should be reversed in order.
'lapp' written backwards gives 'ppal'.
'a'+'ppal'='APPAL'
(Other definitions for appal that I've seen before include "Greatly horrify" , "Disgust" , "expressed dismay" , "Fill with horror" , "exhibiting dismay" .)