= Stygian, adj.

Pertaining to the river Styx, or, in wider sense, to the infernal regions of classical mythology.

Of, relating to, or resembling the mythical fiery river Phlegethon (see Phlegethon, n.); spec. blazing, burning.

Of or relating to the mythical fiery river Phlegethon; = Phlegethontic, adj.