noun

a person believing in or practising religious heresy.

dissident,dissenter,nonconformist,unorthodox thinker,heterodox thinker,apostate,freethinker,iconoclast,schismatic,renegade,disruptor,sceptic,agnostic,atheist,non-theist,non-believer,unbeliever,idolater,idolatress,pagan,heathen,separatist,sectarian,revisionist,tergiversator,recreant,recusant,nullifidian,paynim