1. Hellish
   "Hence loathed Melancholy.../In Stygian cave forlorn" 
2. Dark and dismal as of the rivers Acheron and Styx in Hades
   "upon those roseate lips a Stygian hue"
   - Acheronian, Acherontic

See also: dark, infernal

• unpronounceable
• unproper
• unprophetic
• unpropitious
• unpropitiously
• unpropitiousness
• unprotected
• unprotectedness
• unprotective
• unprotesting
• unprotestingly
• unprovable
• unproved
• unproven
• unprovided for
• unprovocative
• unprovoked
• unprovoking
• unpublishable
• unpublished
• unpunctual
• unpunished
• unpurified
• unputdownable
• Unq