Roll into practice court (8)
I believe the answer is:
tribunal
'court' is the definition.
(I know that court can be written as tribunal)
'roll into practice' is the wordplay.
'roll' becomes 'bun' (synonyms).
'into' means one lot of letters goes inside another.
'practice' becomes 'trial'.
'bun' put into 'trial' is 'TRIBUNAL'.
(Other definitions for tribunal that I've seen before include "examination" , "Special court" , "Hearing" , "Court of arbitration - unlit bar (anag)" , "Assembly to conduct judicial business" .)