Rent out a book on newcomer (7)
I believe the answer is:
entrant
'newcomer' is the definition.
(I know that newcomer can be written as entrant)
'rent out a book' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'book' becomes 'nt' (New Testament).
'rent' anagrammed gives 'entr'.
'entr'+'a'+'nt'='ENTRANT'
'on' acts as a link.
(Other definitions for entrant that I've seen before include "One going in for exam" , "One going in for a race or competition" , "Contestant; starter" , "Competitor; beginner" , "One taking part in a race or competition" .)