Jazz fan entertaining worker, perhaps with a choral composition (7)
I believe the answer is:
cantata
'choral composition' is the definition.
(I've seen this in another clue)
'jazz fan entertaining worker perhaps with a' is the wordplay.
'jazz fan' becomes 'cat' (slang term for a jazz fan).
'entertaining' is an insertion indicator (inviting in, as for dinner).
'worker perhaps' becomes 'ant' (worker is a type of ant).
'with' means one lot of letters go next to another.
'cat' enclosing 'ant' is 'cantat'.
'cantat'+'a'='CANTATA'
(Other definitions for cantata that I've seen before include "Vocal setting of a text (often religious)" , "Oratorio on a sacred theme" , "Vocal composition" , "piece of music" , "Setting of words to music" .)