Allowed chapter one to appear in literature (5)
I believe the answer is:
licit
'allowed' is the definition.
(I've seen this in other clues)
'chapter one to appear in literature' is the wordplay.
'chapter' becomes 'ci' (I can't explain this - if you can you should believe this answer much more).
'one to appear in' is an insertion indicator.
'literature' becomes 'lit' (abbreviation).
'ci' put within 'lit' is 'LICIT'.
(Other definitions for licit that I've seen before include "OK?" , "Legitimate" , "Permitted by law" , "Not forbidden, lawful" , "Allowed as by law, not forbidden" .)