Horrify, dismay (5)
I believe the answer is:
appal
This clue is a double definition.
'horrify' is the first definition.
(I know that horrify can be written as appal)
'dismay' is the second definition.
(I know that dismay can be written as appal)
(Other definitions for appal that I've seen before include "Outrage" , "Scandalise" , "Greatly horrify" , "Greatly dismay" , "To shock, dismay" .)