mystery

Etymology

From Middle English mysterie, from Anglo-Norman misterie (Old French mistere), from Latin mysterium, from Ancient Greek μυστήριον (mustḗrion, “a mystery, a secret, a secret rite”), from μύστης (mústēs, “initiated one”), from μυέω (muéō, “I initiate”), from μύω (múō, “I shut”). Displaced native Old English ġerȳne.

noun

1. Something secret or unexplainable; an unknown.
   The truth behind the events remains a mystery.
   The case was that of a murder. It had an element of mystery about it, however, which was puzzling the authorities. A turban and loincloth soaked in blood had been found; also a staff. 1927, F. E. Penny, chapter 4, in Pulling the Strings
2. Someone or something with an obscure or puzzling nature.
   That man is a mystery.
   Then I had a good think on the subject of the hocussing of Cigarette, and I was reluctantly bound to admit that once again the man in the corner had found the only possible solution to the mystery. 1905, Baroness Emmuska Orczy, chapter 5, in The Hocussing of Cigarette
3. 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.
4. (obsolete) A secret or mystical meaning.
   ...and, not knowing the meaning or misterie of her pollicie, forgat no termes of reproche or rigorous rebuke against his chast doughter. 1567, Matteo Bandello, Certain Tragical Discourses of Bandello, tr. Geffraie Fenton
5. A religious truth not understandable by the application of human reason alone (without divine aid).
   1744 (first printed), Jonathan Swift, A Sermon on the Trinity If God should please to reveal unto us this great mystery of the Trinity, or some other mysteries in our holy religion, we should not be able to understand them, unless he would bestow on us some new faculties of the mind.
6. (archaic outside Eastern Orthodoxy) A sacrament.
   There are seven mysteries, or sacraments, in the Greek church, viz. baptism, the chrism (a rite peculiar to this church), the eucharist, confession, ordination, marriage, and the holy oil. 1809, Sir Robert Ker Porter, Travelling Sketches in Russia and Sweden: During the Years 1805, 1806, 1807, 1808
7. (chiefly in the plural) A secret religious celebration, admission to which was usually through initiation.
   the Eleusinian mysteries
   the Mysteries of Mithras
   It is, indeed, part of the ritual of the candidate for adeptship into the British mysteries, resembling that for the neophyte into the Osirian, Cabiric or Orphean mysteries. 1928, Lewis Spence, Mysteries of Britain, page v. 123
8. (Catholicism) A particular event or series of events in the life of Christ.
   The second decade of the Rosary concerns the Sorrowful mysteries, such as the crucifixion and the crowning with thorns.
9. (archaic) A craft, art or trade; specifically a guild of craftsmen.
   The trades, the crafts, the mysteries, would all be losers. 1776, Adam Smith, An Inquiry into the Nature and Causes of the Wealth of Nations