Stupefied with horror (6)
I believe the answer is:
aghast
'stupefied with horror' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for aghast that I've seen before include "Deeply dismayed" , "Very unhappy" , "Filled with horror or shock" , "Shocked, dumbfounded" , "Appalled, shocked" .)