Piano needed in old-time musical work (5)
I believe the answer is:
opera
'musical work' is the definition.
(operas are musical works)
'piano needed in old-time' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'needed in' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'time' becomes 'era' (an era is a period of time).
'o'+'era'='oera'
'p' placed into 'oera' is 'OPERA'.
(Other definitions for opera that I've seen before include "Eg, Il trovatore" , "Musical in which all the words are sung" , "10 [NORMA], for example" , "art form" , "Macbeth, say" .)