Round fruit, soft (5)
I believe the answer is:
plump
'round' is the definition.
(both can mean fat or chubby)
'fruit soft' is the wordplay.
'fruit' becomes 'plum' (plum is a kind of fruit).
'soft' becomes 'p' (musical abbreviation for 'piano').
'plum'+'p'='PLUMP'
(Other definitions for plump that I've seen before include "Opt - round" , "Having a full rounded shape" , "Chubby, rounded" , "stout" , "Corpulent" .)