Horrify a European after revolution (5)
I believe the answer is:
appal
'horrify' is the definition.
('appal' can be a synonym of 'horrify')
'a european after revolution' is the wordplay.
'european' becomes 'lapp' (Lapp is an example**).
'after revolution' says the letters should be written in reverse.
'lapp' in reverse letter order is 'ppal'.
'a'+'ppal'='APPAL'
(Other definitions for appal that I've seen before include "Disgust" , "To shock, dismay" , "Dismay, horrify" , "Put at rest (suspicion)" , "Cause to be unpleasantly surprised" .)