Definition of: underworld

(un′dər·wûrld′) noun
1. In Greek and Roman mythology, the abode of the dead; Hades; Orcus.
2. In later folklore, sometimes a beautiful country under the earth or sea; also, fairyland, sometimes entered through a well.
3. The antipodes; also, all beneath the horizon.
4. The sublunary world; the earth.
5. The debased, criminal, or degenerate components of the social order; the world of crime and vice; gangsterdom.