One who does not believe in a certain principle.
One who does not believe in a certain religion.
One with no religious beliefs.
Rejecting a specific religion.
Of, characteristic of, or relating to unbelievers or unbelief.
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.
A strict follower of a doctrine.