The body politic of banal prosperity (12)
I believe the answer is:
commonwealth
'the body politic' is the definition.
('commonwealth' can be a synonym of 'body politic')
'banal prosperity' is the wordplay.
'banal' becomes 'common' (I've seen this before).
'prosperity' becomes 'wealth' (I've seen this before).
'common'+'wealth'='COMMONWEALTH'
'of' is the link.
(Other definitions for commonwealth that I've seen before include "such as Virginia" , "Successor to Empire" , "Australia, for example" , "Period following the English Civil Wars" , "Republic" .)