A turnip prepared for zealot (7)
I believe the answer is:
puritan
'for zealot' is the definition.
(thesaurus)
'a turnip prepared' is the wordplay.
'prepared' indicates an anagram.
'a'+'turnip'='aturnip'
'aturnip' is an anagram of 'PURITAN'.
(Other definitions for puritan that I've seen before include "One for whom Shaw wrote" , "Dour Protestant" , "Over-strict moralist" , "Upright" , "Strictly moral person" .)