Bill, popular singer (7)
I believe the answer is:
invoice
'bill' is the definition.
('invoice' can be a synonym of 'bill')
'popular singer' is the wordplay.
'popular' becomes 'in'.
'singer' becomes 'voice' (voice is a kind of singer**).
'in'+'voice'='INVOICE'
(Other definitions for invoice that I've seen before include "Pollen holder" , "ask for payment" , "Statement of account" , "Bill (fit to sing?)" , "Statement for goods" .)