Acheronian Acheronian /ˌækəˈroʊniən/

adjective

1. Dark and dismal as of the rivers Acheron and Styx in Hades  ( Acheronian , Acherontic , Stygian )
   dark and dismal as of the rivers Acheron and Styx in Hades
    In the depths of an Acheronian forest
   in the depths of an Acheronian forest
    Upon those roseate lips a Stygian hue
   upon those roseate lips a Stygian hue