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Adjective: underground  ,ún-du(r)'grawnd
  1. Under the level of the ground
    "underground caverns";
    - belowground
  2. Conducted with or marked by hidden aims or methods
    "underground resistance";
    - clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover
  3. (of music, art, etc) not mainstream; radically new
Noun: underground  ,ún-du(r)'grawnd
  1. A secret group organized to overthrow a government or occupation force
    - resistance
  2. [Brit] An electric railway operating below the surface of the ground (usually in a city)
    "in Paris the subway system is called the 'metro' and in London it is called the 'tube' or the 'underground'";
    - metro, tube [UK], subway system [N. Amer], subway [N. Amer]
Adverb: underground  ,ún-du(r)'grawnd
  1. In or into hiding or secret operation
    "the organization was driven underground"
  2. Beneath the surface of the earth
    "water flowing underground"

Derived forms: undergrounds

See also: covert, subsurface

Type of: rail, railroad [N. Amer], railroad line [N. Amer], railway [Brit, Cdn], railway line [Brit, Cdn], railway system [Brit, Cdn], revolutionary group

Encyclopedia: Underground