Reformist broke car dial (7)
I believe the answer is:
radical
'reformist' is the definition.
(thesaurus)
'broke car dial' is the wordplay.
'broke' indicates an anagram.
'car'+'dial'='cardial'
'cardial' anagrammed gives 'RADICAL'.
(Other definitions for radical that I've seen before include "Deep-seated" , "One seeking root and branch reform" , "Drastic or thorough as changes may be" , "objections to current policy?" , "Going to the root" .)