Debauched book after a number of years (8)
I believe the answer is:
decadent
'debauched' is the definition.
(I've seen this before)
'book after a number of years' is the wordplay.
'book' becomes 'NT' (New Testament).
'after' means one lot of letters go next to another.
'a number of years' becomes 'decade' (I've seen this before).
'nt' after 'decade' is 'DECADENT'.
(Other definitions for decadent that I've seen before include "Rotten" , "Showing moral decline" , "Degenerate" , "Marked by excessive self-indulgence and moral decay" , "Luxuriously self-indulgent" .)