Clever book withdrawn -- morally justified (5)
I believe the answer is:
right
'morally justified' is the definition.
(morally correct)
'clever book withdrawn' is the wordplay.
'clever' becomes 'bright' (bright can mean clever or gifted).
'book' becomes 'b' (abbreviation for book).
'withdrawn' is a deletion indicator.
'bright' with 'b' taken out is 'RIGHT'.
(Other definitions for right that I've seen before include "straight" , "Morally good, justifiable or acceptable" , "one side" , "Morally good; rectify" , "Fit" .)