underworld
noun /ˈʌndəwɜːld/
  /ˈʌndərwɜːrld/
[singular]- the people and activities involved in crime in a particular place
- the criminal underworld
 - the Glasgow underworld
 - the dark underworld of drug abuse and petty crime
 - He ran an import-export business and had underworld contacts in Japan.
 
Oxford Collocations Dictionaryadjective- dark
 - murky
 - seedy
 - …
 
- boss
 - figure
 - contact
 - …
 
- in the… underworld
 
 - the underworld(in myths and legends, for example those of ancient Greece) the place under the earth where people are believed to go when they die
- The three-headed dog Cerberus guarded the entrance to the underworld.