Mystery comes from Greek myein meaning 'to close the lips'. The initiated kept silent about sacred rites on pain of death. A mystery was originally not a puzzle to solve but a secret too dangerous to speak.
Something that is difficult or impossible to understand or explain; a secret religious rite or doctrine.
From Anglo-French misterie, from Latin mystērium, from Greek mystḗrion meaning 'secret rite, secret worship, secret doctrine', from mystēs meaning 'one initiated into the mysteries', from myein meaning 'to close, to shut' — specifically, to close the eyes or lips. The initiated were those who had closed their mouths: sworn to secrecy about what they had witnessed. The Eleusinian Mysteries — ancient Greece's most sacred rites — took their name from this word. Participants were forbidden on pain of death from revealing what happened. The modern