Chapter soon becoming standard? (5)
I believe the answer is:
canon
'standard?' is the definition.
(I've seen this before)
'chapter soon' is the wordplay.
'chapter' becomes 'c' (abbreviation).
'soon' becomes 'anon' (synonyms).
'c'+'anon'='CANON'
'becoming' acts as a link.
(Other definitions for canon that I've seen before include "Cathedral cleric" , "priest for cathedral duties" , "Principle - church dignitary - regulation" , "Body of established rules or principles" , "religious leader" .)