secret

not open or public; kept private or not revealed

• “a secret formula”
• “secret ingredients”
• “secret talks”

conducted with or marked by hidden aims or methods

• “clandestine intelligence operations”
• “cloak-and-dagger activities behind enemy lines”
• “hole-and-corner intrigue”
• “secret missions”
• “a secret agent”
• “secret sales of arms”
• “surreptitious mobilization of troops”
• “an undercover investigation”
• “underground resistance”

not openly made known

• “a secret marriage”
• “a secret bride”

communicated covertly

• “their a secret signal was a wink”
• “secret messages”

not expressed

• “secret (or private) thoughts”

designed to elude detection

• “a hidden room or place of concealment such as a priest hole”
• “a secret passage”
• “the secret compartment in the desk”

hidden from general view or use

• “a privy place to rest and think”
• “a secluded romantic spot”
• “a secret garden”

(of information) given in confidence or in secret

• “closet information”
• “this arrangement must be kept confidential”
• “their secret communications”

indulging only covertly

• “a closet alcoholic”
• “closet liberals”

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

• “mysterious symbols”
• “the mystical style of Blake”
• “occult lore”
• “the secret learning of the ancients”

the next to highest level of official classification for documents

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

• “the combination to the safe was a secret”
• “he tried to keep his drinking a secret”

information known only to a special group

• “the secret of Cajun cooking”

something that baffles understanding and cannot be explained

• “how it got out is a mystery”
• “it remains one of nature”