Surprise delivery service dropping off opposite base (5)
I believe the answer is:
amaze
'surprise' is the definition.
(amazing is a kind of surprising)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for amaze that I've seen before include "Confound with wonder" , "Stagger" , "Floor" , "Flabbergast" , "Affect with wonder" .)