a doctrine held by a member of a religion at variance with established religious beliefs
A controversial or unorthodox opinion held by a member of a group, as in politics, philosophy or science.
A strict follower of a doctrine.
One who believes dogmatically in something regardless of evidence or even conclusive proof that the thing is false or was staged; one who has true-believer syndrome.
Used other than figuratively or idiomatically: see true, believer.