Source : Webster's Revised Unabridged Dictionary (1913)

Acherontic \Ach`e*ron"tic\, a.
   Of or pertaining to Acheron; infernal; hence, dismal, gloomy;
   moribund.

Source : WordNet®

Acherontic
     adj : dark and dismal as of the rivers Acheron and Styx in Hades;
           "in the depths of an Acheronian forest"; "upon those
           roseate lips a Stygian hue"-Wordsworth [syn: {Acheronian},
            {Stygian}]