Rate reform more certain -- official (9)
I believe the answer is:
treasurer
'official' is the definition.
(thesaurus)
'rate reform more certain' is the wordplay.
'reform' indicates anagramming the letters.
'more certain' becomes 'surer' ('sure' can be a synonym of 'certain').
'rate' is an anagram of 'trea'.
'trea'+'surer'='TREASURER'
(Other definitions for treasurer that I've seen before include "Financial administrator" , "Society official" , "Financial controller" , "Club official" , "Financial assets manager" .)