UNDERGROUND

Definition of UNDERGROUND

  1. (noun)a secret group organized to overthrow a government or occupation force
  2. (noun)an electric railway operating below the surface of the ground (usually in a city)
  3. (adj)under the level of the ground
  4. (adj)conducted with or marked by hidden aims or methods
  5. (adv)in or into hiding or secret operation
  6. (adv)beneath the surface of the earth