Overindulgence? Belly filled with large superfluity in the end underlying weight? (8)
I believe the answer is:
gluttony
'overindulgence?' is the definition.
(I've seen this in another clue)
'belly filled with large superfluity in the end underlying weight?' is the wordplay.
'belly' becomes 'gut' (informal term for the stomach or gut).
'filled with' means one lot of letters goes inside another.
'large' becomes 'L' (eg in clothes sizes).
'superfluity in the end underlying weight?' becomes 'tony' (I can't explain this - if you can you should give a lot more credence to this answer).
'gut' going around 'l' is 'glut'.
'glut'+'tony'='GLUTTONY'
Can you help me to learn more?
(Other definitions for gluttony that I've seen before include "bingeing" , "A deadly sin" , "One of the seven deadly sins" , "Greed in eating" , "Habitual greed (for food)" .)