Immoral books hidden by society for years and years (7)
I believe the answer is:
decades
'years and years' is the definition.
(I've seen this in another clue)
'immoral books hidden by society' is the wordplay.
'immoral' becomes 'decadent' (I've seen this before).
'books' becomes 'NT' (New Testament).
'hidden by' indicates named letters should be taken away.
'society' becomes 's' (common abbreviation in names of organisations).
'decadent' with 'nt' taken out is 'decade'.
'decade'+'s'='DECADES'
'for' is the link.
(Other definitions for decades that I've seen before include "10-year periods" , "Ten-year spells" , "Periods of 10 years" , "Ten year periods" .)