English

Definition of underground noun from the Oxford Advanced Learner's Dictionary

     

    underground

     noun
    noun
    BrE BrE//ˈʌndəɡraʊnd//
     
    ; NAmE NAmE//ˈʌndərɡraʊnd//
     
    Trains, Train and bus travel, Terrorism
     
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  1. 1(also the Underground) (British English) (North American English subway) [singular] an underground railway/railroad system in a city underground stations the London Underground I always travel by underground. British/​Americanunderground / subway / metro / tube A city’s underground railway/​railroad system is usually called the underground (often the Underground) in British English and the subway in North American English. Speakers of British English also use subway for systems in American cities and metro for systems in other European countries. The Metro is the name for the systems in Paris and Washington, D.C. London’s system is often called the Tube. compare metro, tube See related entries: Trains, Train and bus travel
  2. 2the underground [singular + singular or plural verb] a secret political organization, usually working against the government of a country See related entries: Terrorism
  3. 3(Indian English) a person who works against the government as a member of a secret political organization
  4. Extra examples I always seem to get lost in the underground. I often travel on the underground. It brought the whole underground system to a halt. We went by underground.
See the Oxford Advanced American Dictionary entry: underground