After a few years, book degenerate (8)
I believe the answer is:
decadent
'degenerate' is the definition.
(I know that degenerate can be written as decadent)
'after a few years book' is the wordplay.
'after' is a charade indicator (letters next to each other).
'a few years' becomes 'decade' (I've seen this before. I am not sure about the 'few' bit.).
'book' becomes 'NT' (New Testament).
'decade' next to 'nt' is 'DECADENT'.
Can you help me to learn more?
(Other definitions for decadent that I've seen before include "Depraved" , "Sybaritic" , "Reflecting cultural decline" , "Decanted in corrupt way" , "Culturally in decline" .)