Daze, stupefy (4)
I believe the answer is:
stun
I believe this clue is a double definition.
'daze' is the first definition.
(I know that daze can be written as stun)
'stupefy' is the second definition.
(I know that stupefy can be written as stun)
(Other definitions for stun that I've seen before include "Shock, flabbergast" , "Daze or bewilder" , "Shock into silence" , "Make dazed or numb" , "'Shock, daze (4)'" .)