Subject still associated with books returned (5)
I believe the answer is:
topic
'subject' is the definition.
(as in a topic for discussion)
'still associated with books returned' is the wordplay.
'still' becomes 'pic' (short for picture).
'associated with' is a charade indicator (letters next to each other).
'books' becomes 'OT' (Old Testament).
'returned' says the letters should be written backwards.
'ot' in reverse letter order is 'to'.
'pic' put after 'to' is 'TOPIC'.
(Other definitions for topic that I've seen before include "Subject matter of a conversation or discussion" , "Something to discuss" , "Question" , "Theme (of, eg, a talk)" , "Subject (of a talk, etc)" .)