1. hellish - "Hence loathed Melancholy.../In Stygian cave forlorn"- Milton • Similar to: infernal 2. 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, Acherontic • Similar to: dark • Derivationally related forms: Acheron (for: Acheronian)