Astonish, stupefy (4)
I believe the answer is:
stun
This clue is a double definition.
'astonish' is the first definition.
(I've seen this before)
'stupefy' is the second definition.
(synonyms)
(Other definitions for stun that I've seen before include "Daze, knock senseless" , "Daze, paralyse" , "Bowl over" , "'Shock, daze (4)'" , "Shock or astonish" .)