Standard chapter, unattributed (5)
I believe the answer is:
canon
'standard' is the definition.
(I've seen this before)
'chapter unattributed' is the wordplay.
'chapter' becomes 'c' (abbreviation).
'unattributed' becomes 'anon'.
'c'+'anon'='CANON'
(Other definitions for canon that I've seen before include "Big type" , "Basic law or principle" , "set of books" , "Churchman" , "Member of a cathedral chapter" .)