Organisation keeping peace in family court (8)
I believe the answer is:
tribunal
'court' is the definition.
('tribunal' can be a synonym of 'court')
'organisation keeping peace in family' is the wordplay.
'organisation keeping peace' becomes 'un' (United Nations).
'in' indicates putting letters inside.
'family' becomes 'tribal' (both can mean relating to one's family).
'un' put into 'tribal' is 'TRIBUNAL'.
(Other definitions for tribunal that I've seen before include "Official board" , "Judgement seat" , "Court, investigative board" , "Hearing" , "Court of justice or arbitration" .)