Bill, a relation (7)
I believe the answer is:
account
I believe this is a double definition.
'bill' is the first definition.
('account' can be a synonym of 'bill')
'a relation' is the second definition.
(account is a kind of relation)
(Other definitions for account that I've seen before include "News report" , "Invoice - story" , "Profitable to turn to this" , "Bill; importance" , "Explanation of conduct" .)