Meaning

noun something that baffles understanding and cannot be explained

noun a story about a crime (usually murder) presented as a novel or play or movie

originFrom 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, “to initiate”), from μύω (múō, “to shut”). Displaced native Old English ġerȳne.

Etymology from Wiktionary, CC BY-SA 3.0