Piano used in old time musical work (5)
I believe the answer is:
opera
'musical work' is the definition.
(operas are musical works)
'piano used in old time' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'used in' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'time' becomes 'era' (era is a kind of time).
'o'+'era'='oera'
'p' inserted inside 'oera' is 'OPERA'.
(Other definitions for opera that I've seen before include "Throw a rope for this show" , "works in Latin" , "Patience, for example" , "Macbeth, perhaps" , "musical presentation" .)