John cheers oratorio (7)
I believe the answer is:
cantata
'oratorio' is the definition.
(synonyms)
'john cheers' is the wordplay.
'john' becomes 'can' (both can informally mean toilet).
'cheers' becomes 'tata' (I can't explain this - if you can you should believe this answer much more).
'can'+'tata'='CANTATA'
Can you help me to learn more?
(Other definitions for cantata that I've seen before include "Vocal-orchestral piece" , "Vocal work with orchestra" , "Musical setting of a text, with arias, recitatives etc" , "Work for accompanied voice" , "One of 200+ by Bach" .)