Chunky mole holding in stomach (6)
I believe the answer is:
stumpy
'chunky' is the definition.
(I know that chunky can be written as stumpy)
'mole holding in stomach' is the wordplay.
'mole' becomes 'spy' (I've seen this in another clue).
'holding in' indicates putting letters inside.
'stomach' becomes 'tum' (synonyms).
'spy' enclosing 'tum' is 'STUMPY'.
(Other definitions for stumpy that I've seen before include "Short and thick" , "pudgy" , "Short and squat" , "Short and thickset" .)