Insincere talk advanced with thanks for choral work (7)
I believe the answer is:
cantata
'choral work' is the definition.
(I've seen this before)
'insincere talk advanced with thanks' is the wordplay.
'insincere talk' becomes 'cant' (I've seen this in another clue).
'advanced' becomes 'a' (abbreviation).
'with' means one lot of letters go next to another.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'cant'+'a'+'ta'='CANTATA'
'for' acts as a link.
(Other definitions for cantata that I've seen before include "aria" , "Work for accompanied voice" , "Choral work" , "Choral item" , "Song" .)