neth·er·world 
/ˈnɛðɚˌwɚld/ noun
plural neth·er·worlds /ˈnɛðɚˌwɚld/ noun 1 the netherworld literary : the world of the dead : hell 2 [count] : a place unknown to most people where secret and often illegal things are done — usually singular ▪ The book describes the author's journey into the netherworld of drug dealers. ▪ a criminal netherworld
