Not believing in God, religion, or a comparable ideology.
Not true to allegiance, duty, or vows
Lacking faith; lacking belief in something.
Unfaithful (said of people, towards their partners)
Serving to disappoint or deceive
Not observant of promises or covenants.
Not practicing; of a person in a particular profession, not engaged in the practice of that profession; of a person born into a particular religion, not abiding by the rituals and mores of that religion.