Regular payment concerning books (4)
I believe the answer is:
rent
'regular payment' is the definition.
(rent is a kind of regular payment)
'concerning books' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'books' becomes 'NT' (New Testament).
're'+'nt'='RENT'
(Other definitions for rent that I've seen before include "opening" , "Torn, due to landlord" , "It's paid by a tenant" , "Payment for accommodation - that's torn it" , "Payment for use of house" .)