noun

• Something secret or unexplainable; an unknown.
• Someone or something with an obscure or puzzling nature.
• An account, story, book, film, or play, often with the theme of crime or murder, with a surprise ending that explains all the strange events that have occurred.
• (obsolete) A secret or mystical meaning.
• A religious truth not understandable by the application of human reason alone (without divine aid).
• (archaic outside Eastern Orthodoxy) A sacrament.
• (chiefly in the plural) A secret religious celebration, admission to which was usually through initiation.
• (Catholicism) A particular event or series of events in the life of Christ.
• (archaic) A craft, art or trade; specifically a guild of craftsmen.