Lodger puts number on a book (6)
I believe the answer is:
tenant
'lodger' is the definition.
(I've seen this before)
'number on a book' is the wordplay.
'number' becomes 'ten' (ten is a kind of number).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'book' becomes 'nt' (New Testament).
'ten'+'a'+'nt'='TENANT'
'puts' is the link.
(Other definitions for tenant that I've seen before include "Renting occupant" , "Occupier of rented property" , "one paying rent" , "his flat?" , "Person renting property" .)