adjective

(1) Not open or public

(2) Not openly made known

(3) Communicated covertly

(4) Not expressed

(5) Designed to elude detection

(6) Hidden from general view or use

(7) (of information) given in confidence or in secret

(8) Indulging only covertly

(9) Having an import not apparent to the senses nor obvious to the intelligence

(10) The next to highest level of official classification for documents

(11) Hidden

(12) Unrevealed

(13) Underhand

(14) Clandestine

noun

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

(2) Information known only to a special group

(3) Something that baffles understanding and cannot be explained

(4) Something kept hidden

(5) Unrevealed