Too much left in the intestine (4)
I believe the answer is:
glut
'too much' is the definition.
(I've seen this in another clue)
'left in the intestine' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in the' indicates putting letters inside.
'intestine' becomes 'gut' (synonyms).
'l' inserted into 'gut' is 'GLUT'.
(Other definitions for glut that I've seen before include "stuff" , "Satiate" , "Flood" , "A surplus or excess" , "Overabundance" .)