Underworld (noun)

1. The world of criminals and organized crime.
2. The realm of the dead in ancient Greek and Roman mythology.
3. The hidden or secret world, especially one associated with crime or vice.

Origin:

Under + world.

Examples:

1. The police were investigating the activities of the local underworld.
2. The underworld figures were known to have a significant influence on the city's politics.
3. In ancient Greek mythology, the underworld is the realm of the dead, ruled by the god Hades.
4. He had a connection to the underworld through his past criminal activities.
5. The story depicts the journey of the protagonist through the dark and dangerous underworld of the city.