STYGIAN, adjective [Latin] Pertaining to Styx, fabled by the ancients to be a river of hell over which the shades of the dead passed, or the region of the dead; hence, hellish; infernal. At that so sudden blaze, the stygian throng bent their aspect.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI