noun Classical Mythology.
Examples from the Web for styx
Fallon wasn't too shabby himself, performing admirable renditions of Iggy Azalea's "Fancy" and Styx's "Mr. Roboto."Viral Video of the Day: Emma Stone's Lip Sync Battle|The Daily Beast Video|April 29, 2014|DAILY BEAST
This great strange goddess had sworn never to love or marry—had sworn it by Styx, I suppose.Gods and Heroes|R. E. Francillon
God, in truth, knows no other judge that can compel him to give what may turn to evil, he is not like Jupiter who fears the Styx.Theodicy|G. W. Leibniz
To-morrow, was it not, that you were to journey to Tyburn and from thence across the Styx?A Daughter of Raasay|William MacLeod Raine
Word Origin for Styx
late 14c., the Greek river of the Underworld, cognate with Greek stygos "hatred," stygnos "gloomy." Oaths sworn by it were supremely binding and even the gods feared to break them. The adjective is Stygian.