secret

Sense 1 noun

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

the combination to the safe was a secret

Sense 2 adjective

not open or public; kept private or not revealed

a secret formula

Sense 3 noun

information known only to a special group

the secret of Cajun cooking

Sense 4 adjective

conducted with or marked by hidden aims or methods

clandestine intelligence operations

Sense 5 noun

something that baffles understanding and cannot be explained

how it got out is a mystery

Sense 6 adjective

not openly made known

a secret marriage

Sense 7 adjective

communicated covertly

their secret signal was a wink

Sense 8 adjective

not expressed

secret (or private) thoughts

Sense 9 adjective

designed to elude detection

a hidden room or place of concealment such as a priest hole

Sense 10 adjective

hidden from general view or use

a privy place to rest and think

Sense 11 adjective

(of information) given in confidence or in secret

this arrangement must be kept confidential

Sense 12 adjective

indulging only covertly

a secret alcoholic

Sense 13 adjective

having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding

mysterious symbols

Sense 14 adjective

the next to highest level of official classification for documents