Alternative form of Stygian (“of or relating to the river Styx”) / (literary) Dark and gloomy. / (literary) Infernal or hellish. / (vision, of a perceived color) Having a luminosity below 0%.

Of, by or relating to the river Styx. / Of, by or relating to the moon Styx. / Alternative form of stygian: dark and gloomy, or infernal and hellish.

(science fiction) An inhabitant of Styx (a moon of Pluto).