Etymology: < classical Latin mystērium secret, (plural) secret rites, in post-classical Latin also mystical or religious truth (Vetus Latina), (plural) Christian rites (late 2nd cent. in Tertullian), the Eucharist, the elements used in the Eucharist (4th cent.) < ancient Greek μυστήριον mystery, secret, (plural) secret rites, implements used in such rites, in Hellenistic Greek also secret revealed by God, mystical truth, Christian rite, sacrament, in Byzantine Greek also the elements used in the Eucharist (4th cent.), probably (compare also μύστης mystes n.) < the base of μύειν to close (the lips or eyes), probably of imitative origin + -τήριον, suffix forming nouns. Influenced in sense also by Middle French mistere mystical significance (1174 in Old French; superseded by form mystère from the 18th cent. onwards), religious truth (c1240), Christian sacrament (13th cent.), secret rite of an ancient religion (15th cent.), something inexplicable or beyond human comprehension (1452). Compare Spanish misterio (1220–50), Catalan misteri (14th cent.), Italian mistero (14th cent.; also attested as misterio), Portuguese mistério (15th cent.).In ancient Greek μυστήριον occurs chiefly in the plural, denoting certain secret religious ceremonies (the most famous being those of Demeter at Eleusis) which were allowed to be witnessed only by the initiated, who were sworn never to disclose their nature (see sense 7a). In the Septuagint the word occurs only in Daniel and the Apocrypha, where it has the sense of ‘secret purpose or counsel’ (especially of a king or of God). This sense is found in the New Testament, where the word also means either a religious truth long kept secret, but now revealed through Christ to his Church, or something of symbolic significance. In later Christian use μυστήριον became equivalent to sacrament n. (in several passages, e.g. Daniel 2:18, the Vulgate renders it by sacramentum , even when it means only ‘secret’; in other passages mysterium is used). In Old French and English the Christian senses of the word appear earliest. In post-classical Latin (from Vetus Latina) the form misterium occurs with the sense ‘ecclesiastical service’ more usually associated with ministerium ministry n. Confusion between mysterium and ministerium in post-classical Latin is not surprising, given the phonetic and semantic similarity between the two words. The distinction between 3 and mystery n.² 1a, and the distinction between 10 and mystery n.² 2, can only be arbitrary from an etymological point of view. In sense 9 after Middle French mistere (1402 in this sense), post-classical Latin mysterium passion play (1521 in Du Cange). It is uncertain whether this sense is at all influenced by or connected with mystery n.² (with reference to the trades of the performers); compare earlier miracle n. in the same sense in French and English. Dict. Older Sc. Tongue also records a form myster , explaining this as a probable back-formation from the Scots plural form mysteris (see e.g. quot. 1588 at sic-like adj.).

Etymology: < post-classical Latin misterium duty, office, service (from 11th cent. in British sources), occupation, trade (from 13th cent. in British sources), guild (from 14th cent. in British sources), altered form of classical Latin ministerium ministry n. by confusion with mystērium mystery n.¹ (see discussion at that entry). Compare mister n.¹In senses 2 and 3 the word may well have been influenced by or confused with mastery n. (see for example quot. a1400 at sense 2a). Compare discussion s.v. mister n.¹ Compare post-classical Latin forms mistera , mestera in senses 2 and 3 (14th–15th cent. in British sources), probably influenced by forms of Anglo-Norman and Old French mester (see mister n.¹).