Insincere talk about a collection of books (4)
I believe the answer is:
cant
'insincere talk' is the definition.
(I've seen this before)
'about a collection of books' is the wordplay.
'about' becomes 'ca' (short for circa).
'a collection of books' becomes 'NT' (New Testament).
'ca'+'nt'='CANT'
(Other definitions for cant that I've seen before include "Inclination" , "List" , "lean over" , "Hypocritical talk; slope" , "Negative-sounding hypocrisy" .)