Fed up with this chatter, a constant for those attending (6,3)
I believe the answer is:
rabbit pie
'those attending' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'fed up with this chatter a constant' is the wordplay.
'fed up' becomes 'pi' (I can't explain this - if you can you should give a lot more credence to this answer).
'with' is a charade indicator (letters next to each other).
'this chatter' becomes 'rabbit' (both can mean to talk excessively).
'a constant' becomes 'e' (mathematics: i.7p).
'pi' after 'rabbit' is 'rabbitpi'.
'rabbitpi'+'e'='RABBIT PIE'
'for' acts as a link.
Can you help me to learn more?
(Another definition for rabbit pie that I've seen is " Traditional country fare".)