Excess left in stomach (4)
I believe the answer is:
glut
'excess' is the definition.
(thesaurus)
'left in stomach' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'stomach' becomes 'gut' (I've seen this before).
'l' put within 'gut' is 'GLUT'.
(Other definitions for glut that I've seen before include "Excess, surfeit" , "A surfeit as of crops" , "Fill to excess" , "Excessively abundant supply" , "An over-supply, harvest surplus" .)