Gaping mouth (3)
I believe the answer is:
maw
'gaping 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 (animal's)" , "gulf" , "Mouth of a voracious animal - or an American mum?" , "Jaws or mouth of a voracious animal" .)