Heresiarch is a term used to describe a person who promotes or creates heresy, or false teachings in a religious context. Synonyms for this word include apostate, dissident, sectarian, and schismatic. An apostate is someone who has abandoned their former beliefs or allegiance, often for a different religious belief or no belief at all. A dissident is someone who disagrees with established beliefs or policies, often within an organization or government. A sectarian is someone who promotes beliefs that are exclusive to a particular group or sect. A schismatic is someone who creates a division or split within a religious community based on differing beliefs or practices.