Employs old piano at first for compositions (6)
I believe the answer is:
opuses
'compositions' is the definition.
('opus' can be a synonym of 'composition')
'employs old piano at first' is the wordplay.
'employs' becomes 'uses' ('use' can be a synonym of 'employ'**).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'piano' becomes 'p'.
'at first' says to put letters next to each other.
'o'+'p'='op'
'uses' after 'op' is 'OPUSES'.
'for' acts as a link.
(Other definitions for opuses that I've seen before include "Musical works" , "pieces of music" .)