Abdomen, soft little protuberance (4)
I believe the answer is:
Here is my best explanation:
'little protuberance' is the definition.
(word for a small hill)
'abdomen soft' is the subsidiary indication.
'abdomen' becomes 'tum'.
'soft' becomes 'p' (musical abbreviation for 'piano'**).
(Another definition for tump that I've seen is "barrow".)