open secret
Something that is widely known, although it is not supposed to be. Oh please, everyone knew he was the real leader of the department—that was like an open secret.
an ˌopen ˈsecret
a fact that is supposed to be a secret but that everyone knows: It’s an open secret that they’re getting married.open secret, an
Something that is supposedly clandestine but is actually well known. This term was used as the Italian title of a play (Il pubblico secrete) translated by Carlo Gozzi in 1769 from a Spanish play by Calderón de la Barca, El secreto a voces (literally, “the noisy secret”). In English it came into general use in the nineteenth century for a secret in name only.