noun something that should remain hidden from others (especially information that is not to be passed on).
noun information known only to a special group.
— synonyms: arcanum
noun something that baffles understanding and cannot be explained.
— synonyms: mystery, enigma, closed_book
adjective not open or public.
adjective conducted with or marked by hidden aims or methods.
— synonyms: clandestine, cloak-and-dagger, hole-and-corner(a), hugger-mugger, hush-hush, surreptitious, undercover, underground
adjective not openly made known.
— synonyms: unavowed
adjective communicated covertly.
adjective not expressed.
— synonyms: private
adjective designed to elude detection.
— synonyms: hidden
adjective hidden from general view or use.
— synonyms: privy, secluded
adjective (of information) given in confidence or in secret.
— synonyms: confidential
adjective indulging only covertly.
adjective having an import not apparent to the senses nor obvious to the intelligence.
— synonyms: mysterious, mystic, mystical, occult, orphic
adjective the next to highest level of official classification for documents.
Examples
“"Can you keep a secret?" "Yes." "So can I."”
“The secret to a long-lasting marriage is compromise.”
“The work was done in secret, so that nobody could object.”