Appal (7)
'appal' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for horrify that I've seen before include "Fill with disgust" , "Appal, alarm" .)
(Other definitions for daunt that I've seen before include "Make (someone) apprehensive" , "Frighten, intimidate" , "Cow" , "Scare off - dismay" , "Dishearten" .)