Bookless characters felt line should be banter (8)
I believe the answer is:
raillery
'banter' is the definition.
(synonyms)
'bookless characters felt line' is the wordplay.
I cannot quite understand how this works, but
'line' could be 'rail' (synonyms) and 'rail' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'should be' acts as a link.
Can you help me to learn more?
(Other definitions for raillery that I've seen before include "Light teasing repartee" , "Satirical banter" , "Good-humoured teasing" , "Banter, back-chat" , "Playful satire" .)