Source : Webster's Revised Unabridged Dictionary (1913)

Darkly \Dark"ly\, adv.
   1. With imperfect light, clearness, or knowledge; obscurely;
      dimly; blindly; uncertainly.

            What fame to future times conveys but darkly down.
                                                  --Dryden.

            so softly dark and darkly pure.       --Byron.

   2. With a dark, gloomy, cruel, or menacing look.

            Looking darkly at the clerguman.      --Hawthorne.

Source : WordNet®

darkly
     adv 1: without light; "the river was sliding darkly under the mist"
            [syn: {in darkness}]
     2: in a dark glowering menacing manner; "he stared darkly at
        her"