anything that is kept secret or remains unexplained or unknown: the mysteries of nature.
any affair, thing, or person that presents features or qualities so obscure as to arouse curiosity or speculation: The masked guest is an absolute mystery to everyone.
a novel, short story, play, or film whose plot involves a crime or other event that remains puzzlingly unsettled until the very end: a mystery by Agatha Christie.
obscure, puzzling, or mysterious quality or character: the mystery of Mona Lisa's smile.
any truth that is unknowable except by divine revelation.