Bawdy old book set (7)
I believe the answer is:
obscene
'bawdy' is the definition.
(I've seen this in another clue)
'old book set' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'book' becomes 'b' (abbreviation for book).
'set' becomes 'scene' (scene is a kind of set).
'o'+'b'+'scene'='OBSCENE'
(Other definitions for obscene that I've seen before include "Offensively vulgar" , "Lewd or loathsome" , "Lewd - offensive" , "Pseudonym" , "Indecent, lewd" .)