Something that is difficult or impossible to understand or explain; chiefly in Christian theology, a religious belief based on divine revelation, especially one regarded as beyond human understanding; an incident in the life of Jesus or of a saint as a focus of devotion in the Roman Catholic Church, especially each of those commemorated during recitation of successive decades of the rosary.
In secular reference, a handicraft or trade, especially when referred to in indentures; the practices, skills, or lore peculiar to a particular trade or activity and regarded as baffling to those without specialized knowledge.
Recorded from Middle English (in the sense ‘mystic presence, hidden religious symbolism’, the word comes via Old French and Latin from Greek mustērion, related to mystic.
mystery play a popular medieval play based on biblical stories or the lives of the saints. Mystery plays were performed by members of trade guilds in Europe from the 13th century, in churches or later on wagons or temporary stages along a route, frequently introducing apocryphal and satirical elements. Several cycles of plays survive in association with particular English cities and towns.
mystery religion a religion centred on secret or mystical rites for initiates, especially any of a number of cults popular during the late Roman Empire.