The Collaborative International Dictionary of English v.0.48:

Secret \Se"cret\, a. [F. secret (cf. Sp. & Pg. secreto, It.
   secreto, segreto), fr. L. secretus, p. p. of secernere to put
   apart, to separate. See Certain, and cf. Secrete,
   Secern.]
   1. Hidden; concealed; as, secret treasure; secret plans; a
      secret vow. --Shak.
      [1913 Webster]

            The secret things belong unto the Lord our God; but
            those things which are revealed belong unto us.
                                                  --Deut. xxix.
                                                  29.
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   2. Withdrawn from general intercourse or notice; in
      retirement or secrecy; secluded.
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            There, secret in her sapphire cell,
            He with the Nais wont to dwell.       --Fenton.
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   3. Faithful to a secret; not inclined to divulge or betray
      confidence; secretive. [R.]
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            Secret Romans, that have spoke the word,
            And will not palter.                  --Shak.
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   4. Separate; distinct. [Obs.]
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            They suppose two other divine hypostases superior
            thereunto, which were perfectly secret from matter.
                                                  --Cudworth.
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   Syn: Hidden; concealed; secluded; retired; unseen; unknown;
        private; obscure; recondite; latent; covert;
        clandestine; privy. See Hidden.
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The Collaborative International Dictionary of English v.0.48:

Secret \Se"cret\, n. [F. secret (cf. Pr. secret, Sp. & Pg.
   secreto, It. secreto, segreto), from L. secretum. See
   Secret, a.]
   1. Something studiously concealed; a thing kept from general
      knowledge; what is not revealed, or not to be revealed.
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            To tell our own secrets is often folly; to
            communicate those of others is treachery. --Rambler.
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   2. A thing not discovered; what is unknown or unexplained; a
      mystery.
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            All secrets of the deep, all nature's works.
                                                  --Milton.
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   3. pl. The parts which modesty and propriety require to be
      concealed; the genital organs.
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   In secret, in a private place; in privacy or secrecy; in a
      state or place not seen; privately.
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            Bread eaten in secret is pleasant.    --Prov. ix.
                                                  17.
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The Collaborative International Dictionary of English v.0.48:

Secret \Se"cret\, v. t.
   To keep secret. [Obs.] --Bacon.
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The Collaborative International Dictionary of English v.0.48:

classified \classified\ adj.
   1. arranged into classes or categories; as, unclassified.

   Syn: categorized.
        [WordNet 1.5 +PJC]

   2. assigned to a class of documents withheld from general
      circulation; -- of information or documents. Opposite of
      unclassified.

   Note: [Narrower terms: eyes-only; confidential;
         restricted; secret; sensitive; top-secret]
         [WordNet 1.5]

WordNet (r) 3.0 (2006):

secret
    adj 1: not open or public; kept private or not revealed; "a
           secret formula"; "secret ingredients"; "secret talks"
    2: 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" [syn: clandestine,
       cloak-and-dagger, hole-and-corner(a), hugger-mugger,
       hush-hush, secret, surreptitious, undercover,
       underground]
    3: not openly made known; "a secret marriage"; "a secret bride"
       [syn: unavowed, secret]
    4: communicated covertly; "their secret signal was a wink";
       "secret messages"
    5: not expressed; "secret (or private) thoughts" [syn: secret,
       private]
    6: 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" [syn: hidden, secret]
    7: hidden from general view or use; "a privy place to rest and
       think"; "a secluded romantic spot"; "a secret garden" [syn:
       privy, secluded, secret]
    8: (of information) given in confidence or in secret; "this
       arrangement must be kept confidential"; "their secret
       communications" [syn: confidential, secret]
    9: indulging only covertly; "a secret alcoholic"
    10: 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" [syn: mysterious,
        mystic, mystical, occult, secret, orphic]
    11: the next to highest level of official classification for
        documents
    n 1: 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"
    2: information known only to a special group; "the secret of
       Cajun cooking" [syn: secret, arcanum]
    3: something that baffles understanding and cannot be explained;
       "how it got out is a mystery"; "it remains one of nature's
       secrets" [syn: mystery, enigma, secret, closed book]