Synonyms of 'underworld'
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In Greek mythology, Hades was a place under the earth where people went after they died.
Zeus finally sent Hermes to Hades with a request to return the maiden.
Don't worry about going to Hell, just be good.
fire and brimstone
the bottomless pit
the nether world
the lower world
the infernal regions
the bad fire (informal)
the abode of the damned
Thesaurus for underworld from the Collins English Thesaurus
The underworld in a city is the organized crime there and the people who are involved in it.