Amateur still getting to grips with old piano (8)
I believe the answer is:
inexpert
'amateur' is the definition.
(thesaurus)
'still getting to grips with old piano' is the wordplay.
'still' becomes 'inert' (I've seen this before**).
'getting to grips with' indicates putting letters inside.
'old' becomes 'ex'.
'piano' becomes 'p'.
'ex'+'p'='exp'
'inert' going around 'exp' is 'INEXPERT'.
(Other definitions for inexpert that I've seen before include "Inept rex may be lacking in skill" , "Offering little professionally" , "Unskilled" , "not clever" , "Clumsy" .)