Big mouth (3)
I believe the answer is:
maw
'big mouth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for maw that I've seen before include "Jaws or throat of a voracious animal" , "Mouth of a voracious animal - or an American mum?" , "Crop of an animal" , "Jaws or gullet of a voracious animal" , "Jaws or mouth of a voracious animal" .)