More than one doctor sounds like a duck (6)
I believe the answer is:
quacks
I believe this is a double definition.
'more than one doctor' is the first definition.
(quack is a kind of doctor)
'sounds like a duck' is the second definition.
(I've seen this before)
(Other definitions for quacks that I've seen before include "Bad doctors or duck sounds" , "bird sounds" , "Ducks' noises" , "Makes sounds like a duck" , "Duck sounds or dud doctors" .)