Leave dumbfounded (5)
I believe the answer is:
amaze
'leave dumbfounded' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amaze that I've seen before include "Flummox" , "Greatly surprise, astound" , "shock" , "Cause wonder" , "Greatly surprise, fill with wonder" .)