Belly laugh (6)
I believe the answer is:
'belly laugh' is the definition.
(I know that belly laugh can be written as guffaw)
This is all the clue.
(Other definitions for guffaw that I've seen before include "A coarse noisy laugh" , "Roar of laughter" , "A loud vulgar laugh" , "Belly laugh" , "Crude and boisterous laugh" .)