The Collaborative International Dictionary of English v.0.48:

Dark \Dark\ (d[aum]rk), a. [OE. dark, derk, deork, AS. dearc,
   deorc; cf. Gael. & Ir. dorch, dorcha, dark, black, dusky.]
   1. Destitute, or partially destitute, of light; not
      receiving, reflecting, or radiating light; wholly or
      partially black, or of some deep shade of color; not
      light-colored; as, a dark room; a dark day; dark cloth;
      dark paint; a dark complexion.
      [1913 Webster]

            O dark, dark, dark, amid the blaze of noon,
            Irrecoverably dark, total eclipse
            Without all hope of day!              --Milton.
      [1913 Webster]

            In the dark and silent grave.         --Sir W.
                                                  Raleigh.
      [1913 Webster]

   2. Not clear to the understanding; not easily seen through;
      obscure; mysterious; hidden.
      [1913 Webster]

            The dark problems of existence.       --Shairp.
      [1913 Webster]

            What may seem dark at the first, will afterward be
            found more plain.                     --Hooker.
      [1913 Webster]

            What's your dark meaning, mouse, of this light word?
                                                  --Shak.
      [1913 Webster]

   3. Destitute of knowledge and culture; in moral or
      intellectual darkness; unrefined; ignorant.
      [1913 Webster]

            The age wherein he lived was dark, but he
            Could not want light who taught the world to see.
                                                  --Denhan.
      [1913 Webster]

            The tenth century used to be reckoned by medi[ae]val
            historians as the darkest part of this intellectual
            night.                                --Hallam.
      [1913 Webster]

   4. Evincing black or foul traits of character; vile; wicked;
      atrocious; as, a dark villain; a dark deed.
      [1913 Webster]

            Left him at large to his own dark designs. --Milton.
      [1913 Webster]

   5. Foreboding evil; gloomy; jealous; suspicious.
      [1913 Webster]

            More dark and dark our woes.          --Shak.
      [1913 Webster]

            A deep melancholy took possesion of him, and gave a
            dark tinge to all his views of human nature.
                                                  --Macaulay.
      [1913 Webster]

            There is, in every true woman-s heart, a spark of
            heavenly fire, which beams and blazes in the dark
            hour of adversity.                    --W. Irving.
      [1913 Webster]

   6. Deprived of sight; blind. [Obs.]
      [1913 Webster]

            He was, I think, at this time quite dark, and so had
            been for some years.                  --Evelyn.
      [1913 Webster]

   Note: Dark is sometimes used to qualify another adjective;
         as, dark blue, dark green, and sometimes it forms the
         first part of a compound; as, dark-haired, dark-eyed,
         dark-colored, dark-seated, dark-working.
         [1913 Webster]

   A dark horse, in racing or politics, a horse or a candidate
      whose chances of success are not known, and whose
      capabilities have not been made the subject of general
      comment or of wagers. [Colloq.]

   Dark house, Dark room, a house or room in which madmen
      were confined. [Obs.] --Shak.

   Dark lantern. See Lantern. -- The

   Dark Ages, a period of stagnation and obscurity in
      literature and art, lasting, according to Hallam, nearly
      1000 years, from about 500 to about 1500 A. D.. See
      Middle Ages, under Middle.

   The Dark and Bloody Ground, a phrase applied to the State
      of Kentucky, and said to be the significance of its name,
      in allusion to the frequent wars that were waged there
      between Indians.

   The dark day, a day (May 19, 1780) when a remarkable and
      unexplained darkness extended over all New England.

   To keep dark, to reveal nothing. [Low]
      [1913 Webster]