something not understood or beyond understanding: ENIGMA. a piece of fiction dealing usually with the solution of a mysterious crime. the secret or specialized practices or ritual peculiar to an occupation or a body of people. obsolete: a private secret. profound, inexplicable, or secretive quality or character. a religious truth that one can know only by revelation and cannot fully understand. any of the 20 events (such as the Nativity, the Crucifixion, or the Assumption) serving as a subject for meditation during the saying of the rosary. a Christian sacrament. a secret religious rite believed (as in Eleusinian and Mithraic cults) to impart enduring bliss to the initiate. a cult devoted to such rites. MYSTERY PLAY. TRADE, CRAFT. a body of persons engaged in a particular trade, business, or profession: GUILD.