Stomach feeble returning musical phrase (7)
I believe the answer is:
midriff
'stomach' is the definition.
(I've seen this before)
'feeble returning musical phrase' is the wordplay.
'feeble' becomes 'dim' (both can mean faint).
'returning' says the letters should be written in reverse.
'musical phrase' becomes 'riff' (repeated musical phrase).
'dim' back-to-front is 'mid'.
'mid'+'riff'='MIDRIFF'
(Other definitions for midriff that I've seen before include "Part of body between waist and chest" , "Area between stomach and chest" , "Part of torso" , "Region between chest and waist" , "Central part of human body" .)