Source : Webster's Revised Unabridged Dictionary (1913)

Darkling \Dark"ling\, adv. [Dark + the adverbial suffix -ling.]
   In the dark. [Poetic]

         So, out went the candle, and we were left darkling.
                                                  --Shak.

         As the wakeful bird Sings darkling.      --Milton.

Darkling \Dark"ling\, p. pr. & a.
   1. Becoming dark or gloomy; frowing.

            His honest brows darkling as he looked towards me.
                                                  --Thackeray.

   2. Dark; gloomy. ``The darkling precipice.'' --Moore.

Source : WordNet®

darkling
     adj 1: uncannily or threateningly dark or obscure; "a darkling
            glance"; "secret operatives and darkling
            conspiracies"-Archibald MacLeish
     2: (poetic) occurring in the dark or night; "a darkling
        journey"