Name taken from traditional rules of behaviour (5)
I believe the answer is:
ethic
'rules of behaviour' is the definition.
(ethics or morals)
'name taken from traditional' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'taken from' is a deletion indicator.
'traditional' becomes 'ethnic' (eg ethnic dress).
'ethnic' with 'n' removed is 'ETHIC'.
(Other definitions for ethic that I've seen before include "type of behaviour" , "Moral system" , "Ideology" , "Principles accepted by a social group" , "System of principles" .)