Underworld :  (noun)
1: the criminal class
2: (religion) the world of the dead; "he didn't want to go to hell when he died" [syn: Hel, Hell, Hades, infernal region, netherworld, Scheol]

Abaddon, Black Hand, Cosa Nostra, Dis, Gehenna, Hades, Hell, Naraka, Orcus, Pandemonium, Sheol, Tophet, abyss, avichi, bottomless pit, bowels, criminals, deep space, deeps, depths, gangdom, gangland, gaping depths, hades, hell, infernal pit, infernal regions, inferno, jahannan, limbo, lower world, nether world, netherworld, organized crime, outer space, perdition, place of torment, purgatory, shades below, the Mafia, the abyss, the bottomless pit, the grave, the mob, the pit, the rackets, the syndicate, the underworld, unfathomed deeps, unknown depths,