Pertaining to the Styx, a river, according to the ancient myth, flowing around the lower world, the waters of which were used as a symbol in the most binding oaths of the gods.
Hence Infernal; hellish: as, Stygian vapors; a Stygian pool.
the GNU version of the Collaborative International Dictionary of English
adjective.
Of or pertaining to the river Styx; hence, hellish; infernal. See Styx.