Kept hidden from knowledge or view; concealed. Dependably discreet. Operating in a hidden or confidential manner: a secret agent. Not expressed; inward: their secret thoughts. Not frequented; secluded: wandered about the secret byways of Paris. Known or shared only by the initiated: secret rites. Beyond ordinary understanding; mysterious. Containing information, the unauthorized disclosure of which poses a grave threat to national security. Something kept hidden from others or known only to oneself or to a few. Something that remains beyond understanding or explanation; a mystery. A method or formula on which success is based: The secret of this dish is in the sauce. A variable prayer said after the Offertory and before the Preface in the Mass.