Duck sound (5)
I believe the answer is:
quack
'duck sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for quack that I've seen before include "Duck's cry or dud doctor" , "Charlatan - cry of duck" , "Noise of a duck" , "Unqualified man" , "may get called across the pond" .)