Cautious papa with dirty books (7)
I believe the answer is:
prudent
'cautious' is the definition.
(I've seen this before)
'papa with dirty books' is the wordplay.
'papa' becomes 'P' (phonetic alphabet: alpha, bravo, charlie etc.).
'with' means one lot of letters go next to another.
'dirty' becomes 'rude' (I've seen this before).
'books' becomes 'NT' (New Testament).
'p'+'rude'+'nt'='PRUDENT'
(Other definitions for prudent that I've seen before include "Showing care and thought for the future" , "not taking any risks?" , "caution" , "Acting with care for the future" , "Cautious; discreet" .)