Horrify, stun (5)
I believe the answer is:
shock
I believe this is a double definition.
'horrify' is the first definition.
(shocking is a kind of horrifying)
'stun' is the second definition.
(synonyms)
(Other definitions for shock that I've seen before include "Mass of hair; group of sheaves" , "Perturb" , "Outrageous" , "See 18" , "Appal" .)