mys·ter·y 1 
(mĭstə-rē)
(mĭstə-rē)n. pl. mys·ter·ies
1. One that is not fully understood or that baffles or eludes the understanding; an enigma: How he got in is a mystery.
2. One whose identity is unknown and who arouses curiosity: The woman in the photograph is a mystery.
3. A mysterious character or quality: a landscape with mystery and charm.
4. Something that is a secret: "From the first, some private trouble weighed on his mind, and since he chose to make a mystery of its cause, a biographer is bound to respect his wish" (Henry Adams).
5.
a. A work of fiction, such as a novel or a movie, that has a story centered around solving a puzzling crime or mysterious event.
b. A nonfictional account of a puzzling crime or mysterious event presented in the manner of a mystery.
6.
a. A religious cult practicing secret rites to which only initiates are admitted.
b. A secret rite of such a cult.
7. A religious truth that is incomprehensible to reason and knowable only through divine revelation.
8. Christianity
a. An incident from the life of Jesus, especially the Incarnation, Passion, Crucifixion, or Resurrection, of particular importance for redemption.
b. One of the 15 incidents from the lives of Jesus or the Blessed Virgin Mary, such as the Annunciation or the Ascension, serving in Roman Catholicism as the subject of meditation during recitation of the rosary.
9.
a. also Mystery One of the sacraments, especially the Eucharist.
b. mysteries The consecrated elements of the Eucharist.
10. often mysteries The skills, lore, or practices that are peculiar to a particular activity or group and are regarded as the special province of initiates: the mysteries of Freemasonry; the mysteries of cooking game.
11. A mystery play.
[Middle English misterie, from Latin mystērium, from Greek mustērion, secret rite, from mustēs, an initiate, from mūein, to close the eyes, initiate. Senses 8, 9, and perhaps 10, partly from Middle English misterie, occupation, craft-guild; see MYSTERY2.]