An expense to duck, perhaps? (4)
I believe the answer is:
bill
'an expense' is the definition.
(I know that bill is a type of expense)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for bill that I've seen before include "Little William" , "Law proposal" , "one settles with in America?" , "announce" , "The point of anchor?" .)