mystery (n.1)

late 14c., mewet "silent, not speaking," from Old French muet "dumb, mute" (12c.), diminutive of mut, mo, from Latin mutus "silent, speechless, dumb," probably from imitative base *meue- (source also of Sanskrit mukah "dumb," Greek myein "to be shut," of the mouth). Form assimilated in 16c. to Latin mutus. The meaning "incapable of utterance, dumb" is by mid-15c.

c. 1200, ministerie, "the office or function of a priest, a position in a church or monastery; service in matters of religion," from Old French menistere "service, ministry; position, post, employment" and directly from Latin ministerium "office, service, attendance, ministry," from minister "inferior, servant, priest's assistant" (see minister (n.)).

From late 14c. as "personal service or aid." From 1560s as "the body of ministers of religion, the clerical class." From 1710 as "the body of ministers of state in a country." It began to be used 1916 in the names of certain departments in the British government.