Judge rarebit cooked (7)
I believe the answer is:
arbiter
'judge' is the definition.
(thesaurus)
'rarebit cooked' is the wordplay.
'cooked' indicates anagramming the letters.
'rarebit' is an anagram of 'ARBITER'.
(Other definitions for arbiter that I've seen before include "Settler of dispute" , "Judge, final authority" , "expert" , "Judge, adjudicator" , "Ref" .)