Question on advanced books to one side (6)
I believe the answer is:
askant
'one side' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?
'question on advanced books' is the wordplay.
'question' becomes 'ask' (asking a question).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'advanced' becomes 'a' (abbreviation).
'books' becomes 'NT' (New Testament).
'ask'+'a'+'nt'='ASKANT'
'to' is the link.
Can you help me to learn more?
(Other definitions for askant that I've seen before include "With an oblique glance" , "Showing doubt" , "showing suspicion" , "regarded thus with suspicion" , "Mistrustfully" .)