Amaze, stagger (4)
I believe the answer is:
stun
This clue is a double definition.
'amaze' is the first definition.
(to stun is to amaze or shock)
'stagger' is the second definition.
(both can mean to shock)
(Other definitions for stun that I've seen before include "Render semi-conscious with blow" , "Daze, render semi-conscious" , "Daze with nuts" , "Confound" , "Render insensitive" .)