'Underground' definitions:

Definition of 'underground'

From: WordNet
adverb
In or into hiding or secret operation; "the organization was driven underground"
adverb
Beneath the surface of the earth; "water flowing underground"
adjective
Under the level of the ground; "belowground storage areas"; "underground caverns" [syn: belowground, underground]
adjective
Conducted with or marked by hidden aims or methods; "clandestine intelligence operations"; "cloak-and-dagger activities behind enemy lines"; "hole-and-corner intrigue"; "secret missions"; "a secret agent"; "secret sales of arms"; "surreptitious mobilization of troops"; "an undercover investigation"; "underground resistance" [syn: clandestine, cloak-and-dagger, hole-and-corner(a), hugger-mugger, hush-hush, secret, surreptitious, undercover, underground]
noun
A secret group organized to overthrow a government or occupation force [syn: underground, resistance]
noun
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'" [syn: metro, tube, underground, subway system, subway]

Definition of 'Underground'

From: GCIDE
  • Underground \Un"der*ground`\, n.
  • 1. The place or space beneath the surface of the ground; subterranean space. [1913 Webster]
  • A spirit raised from depth of underground. --Shak. [1913 Webster]
  • 2. a subway or subway system, especially in the United Kingdom. [chiefly British] [PJC]
  • 3. a secret organization opposed to the prevailing government; as, the French underground during the Nazi occupation. [PJC]
  • 4. a group or movement holding unorthodox views in an environment where conventional ideas dominate, as in artistic circles. [PJC]

Definition of 'Underground'

From: GCIDE
  • Underground \Un"der*ground`\, a.
  • 1. Being below the surface of the ground; as, an underground story or apartment. [1913 Webster]
  • 2. Done or occurring out of sight; secret. [Colloq.] [1913 Webster]
  • Underground railroad or Underground railway. See under Railroad. [1913 Webster]

Definition of 'Underground'

From: GCIDE
  • Underground \Un"der*ground`\, adv. Beneath the surface of the earth. [1913 Webster]

Definition of 'underground'

From: GCIDE
  • Subway \Sub"way`\, n.
  • 1. An underground way or gallery; especially, a passage under a street, in which water mains, gas mains, telegraph wires, etc., are conducted. [1913 Webster]
  • 2. An underground railroad, usually having trains powered by electricity provided by an electric line running through the underground tunnel. It is usually confined to the center portion of cities; -- called also tube, and in Britain, underground. In certain other countries (as in France or Russia) it is called the metro. [PJC]

Synonyms of 'underground'

From: Moby Thesaurus