Corporation (3)
'corporation' is the definition.
(both can humorously mean belly fat)
This is all the clue.
(Other definitions for gut that I've seen before include "Part of the alimentary canal" , "Stomach, belly" , "(Remove) intestines" , "Remove innards from" , "Material in part of racket" .)
(Other definitions for tum that I've seen before include "Belly" , "Stomach (informal)" , "Corporation" , "Middle" .)