Rash little rascal with naughty books (9)
I believe the answer is:
imprudent
'rash' is the definition.
(similar in meaning)
'little rascal with naughty books' is the wordplay.
'little rascal' becomes 'imp' (imp can mean a misbehaving child).
'with' is a charade indicator (letters next to each other).
'naughty' becomes 'rude' (both can mean indecent).
'books' becomes 'NT' (New Testament).
'imp'+'rude'+'nt'='IMPRUDENT'
(Other definitions for imprudent that I've seen before include "Rash, lacking discretion" , "Without forethought" , "Incautious" , "not wise" , "Reckless" .)