"pertaining to Styx or the nether world," 1560s, from Latin Stygius, from Greek Stygios, from Styx (genitive Stygos); see Styx.
Entries linking to stygian
Styx
late 14c., the Greek river of the Underworld, literally "the Hateful," cognate with Greek stygos "hatred," stygnos "gloomy," from stygein "to hate, abominate," from PIE *stug-, extended form of root *steu- (1) "to push, stick, knock, beat." Oaths sworn by it were supremely binding and even the gods feared to break them. The adjective is Stygian.