Erebus, er'e-bus, in Greek mythology, the son of Chaos and brother of Night. The word signifies impenetrable darkness, and was used to designate the gloomy cavern which must be traversed before the shades reached Hades. In the Odyssey and by later writers it is used as synonymous with Hades. The word has come to be symbolical of darkness. "Dark as Erebus," says Shakespeare.