Horrifies (6)
I believe the answer is:
appals
'horrifies' is the definition.
('appal' can be a synonym of 'horrify')
This is the entire clue.
(Other definitions for appals that I've seen before include "Fills with disgust" , "Fills with dismay or horror (6)" , "'Horrifies, outrages (6)'" , "Shocks" .)