Old American on piano gets work (4)
I believe the answer is:
opus
'work' is the definition.
(I've seen this before)
'old american on piano' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'american' becomes 'us' (abbreviation for United States).
'on' is a charade indicator (letters next to each other).
'piano' becomes 'p' (musical abbreviation).
'us' after 'p' is 'pus'.
'o'+'pus'='OPUS'
'gets' is the link.
(Other definitions for opus that I've seen before include "Work or composition, usually musical" , "A Latin work" , "(Numbered) musical composition" , "Composition - magnum __" , "Musical composition in the soup" .)