Having one of the highest secrecy classifications, "top secret".

Information that is widely known, but not acknowledged openly. / (dated) Information that is not widely known, despite being freely available.

The voting system involving ballots available only at official polling places, prepared at public expense, containing the names of all candidates, and marked in secret at the polling places.

plural of secret admirer

plural of open secret

plural of secret Santa

A governmental agency that deals with espionage and other acts of secrecy.

A supposed secret known to everyone.

plural of secret of Polichinelle

plural of secret agent