Send reeling (4)
I believe the answer is:
stun
'send reeling' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stun that I've seen before include "Dumbfound" , "Concuss, stupefy" , "Make dazed or numb" , "deliver a knock-out blow" , "Make senseless or dizzy with a blow" .)