Battered piano, missing note, embodying something obliterating musical form (5,5)
I believe the answer is:
opera seria
'musical form' is the definition.
(term for a serious opera)
'battered piano missing note embodying something obliterating' is the wordplay.
'battered piano missing note' becomes 'opia' (I can't explain this - if you can you should believe this answer much more).
'embodying' indicates putting letters inside (to embody can mean to contain or include).
'something obliterating' becomes 'eraser' (something which erases or obliterates).
'opia' enclosing 'eraser' is 'OPERA SERIA'.
Can you help me to learn more?
(Another definition for opera seria that I've seen is " Serious stage work, repose aria (anag.)".)