Stupefy in a most unusual way (4)
I believe the answer is:
stun
'stupefy' is the definition.
(I know that stupefy can be written as stun)
'in a most unusual way' is the wordplay.
'in' indicates a hidden word.
'STUN' can be found hidden inside 'most unusual way'.
(Other definitions for stun that I've seen before include "Surprise greatly, knock someone''s socks off" , "Daze with nuts" , "Daze, paralyse" , "Leave speechless" , "Make dazed or numb" .)