Individual rule accordingly adopted by writer (6)
I believe the answer is:
person
'individual' is the definition.
(synonyms)
'rule accordingly adopted by writer' is the wordplay.
'rule' becomes 'r' (legal abbreviation).
'accordingly' becomes 'so' (synonyms).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'writer' becomes 'pen' (something which writes).
'r'+'so'='rso'
'rso' put into 'pen' is 'PERSON'.
(Other definitions for person that I've seen before include "A man or woman" , "Individual human being" , "character" , "See 17" , "present appearing in this" .)