A fat, soft clod (5)
I believe the answer is:
plump
'a fat' is the definition.
(I've seen this before)
'soft clod' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'clod' becomes 'lump' (synonyms).
'p'+'lump'='PLUMP'
(Other definitions for plump that I've seen before include "Full of figure" , "Slightly fat" , "Fat - set down unceremoniously" , "Portly" , "Chubby, rounded" .)