Meaning

noun something that should remain hidden from others (especially information that is not to be passed on)

noun information known only to a special group

noun something that baffles understanding and cannot be explained

originFrom Middle English secrette, from Old French secret, from Latin sēcrētus (“separated, hidden”), from ptp of sēcernō (“separate, to set aside, sunder out”), from cernō, from Proto-Indo-European *krey-. Displaced Old English dēagol (“secret”).

Etymology from Wiktionary, CC BY-SA 3.0