Origins
A mystery was once something you could be executed for discussing.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ The word comes from Greek mystαΈrion, meaning 'secret rite', from mystΔs ('one initiated'), from myein β 'to close'. Specifically: to close the lips.
The Eleusinian Mysteries, held annually near Athens for nearly two thousand years, were the most sacred rites in the Greek world. Initiates witnessed secret ceremonies honouring Demeter and Persephone. What exactly happened inside the Telesterion hall at Eleusis remains unknown β because the penalty for revealing it was death. The silence held so well that, despite thousands of participants over centuries, the core ritual was never recorded.
Alcibiades, the Athenian general, was accused in 415 BCE of profaning the mysteries at a private dinner party. The scandal contributed to his exile and the unravelling of Athens's Sicilian expedition.
Latin Roots
Christian theology adopted mystΔrium to describe truths beyond human understanding β the mystery of the Trinity, the mystery of the Incarnation. Medieval mystery plays took their name from a different word entirely (Latin ministerium, 'ministry'), but the spelling collision merged the two concepts in popular imagination.
The modern detective mystery β the whodunit β is a gentle echo of the original. Where the Greek mysterion was a secret too sacred to reveal, a modern mystery is a puzzle that begs to be solved.