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.
      [1913 Webster]

            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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WordNet (r) 3.0 (2006):

in secret
    adv 1: in secrecy; not openly; "met secretly to discuss the
           invasion plans"; "the children secretly went to the
           movies when they were supposed to be at the library";
           "they arranged to meet in secret" [syn: secretly, in
           secret, on the Q.T., on the QT]