underground

American  

[uhn-der-ground, uhn-der-ground] / ˈʌn dərˈgraʊnd, ˈʌn dərˌgraʊnd /

adverb

1. beneath the surface of the ground.

   traveling underground by subway.

2. in concealment or secrecy; not openly.

   subversion carried on underground.

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adjective

1. existing, situated, operating, or taking place beneath the surface of the ground.

2. used, or for use, underground.

3. hidden or secret; not open.

   underground political activities.

4. published or produced by political or social radicals or nonconformists.

   an underground newspaper.

5. avant-garde; experimental.

   an underground movie.

6. critical of or attacking the established society or system.

   underground opinion.

7. of or for nonconformists; unusual.

   an underground vegetarian restaurant.

noun

1. the place or region beneath the surface of the ground.

2. an underground space or passage.

3. a secret organization fighting the established government or occupation forces.

   He fought in the French underground during the Nazi occupation of France.

4. (often initial capital letter) a movement or group existing outside the establishment and usually reflecting unorthodox, avant-garde, or radical views.

5. Chiefly British. a subway system.

verb (used with object)

1. to place beneath the surface of the ground.

   to underground utility lines.

underground British  

adjective

1. occurring, situated, or used below ground level

   an underground tunnel

   an underground explosion

2. secret; hidden

   underground activities

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adverb

1. going below ground level

   the tunnel led underground

2. into hiding or secrecy

   the group was driven underground

noun

1. a space or region below ground level

2. 1. a movement dedicated to overthrowing a government or occupation forces, as in the European countries occupied by the German army in World War II

   2. ( as modifier )

      an underground group

3. US and Canadian equivalent: subway.  an electric passenger railway operated in underground tunnels

4. (usually preceded by the)

   1. any avant-garde, experimental, or subversive movement in popular art, films, music, etc

   2. ( as modifier )

      the underground press

      underground music

Etymology

Origin of underground

First recorded in 1565–75; under- + ground ¹

Example Sentences

Six days after Noah's disappearance, his body was found in an underground drainage system more than six hundred metres downstream from the culvert inlet which is located behind homes at Northwood Road.

From BBC • May 8, 2026

On an underground train en route to Piccadilly Circus, I got the picture after spotting a newspaper headline.

From The Wall Street Journal • May 7, 2026

Fisk’s authoritarian tactics and campaign targeting vigilantes pushes Daredevil underground to try to assemble allies in order to bring the Kingpin down.

From Los Angeles Times • May 6, 2026

These systems would draw on the underground water to regulate indoor temperatures, offering heating in colder months and cooling during warmer periods.

From Science Daily • May 6, 2026

Kennedy had ordered the resumption of underground testing of H-bombs in September, and he wanted a better understanding of the dangers of fallout.

From "Fallout: Spies, Superbombs, and the Ultimate Cold War Showdown" by Steve Sheinkin

Related Words

• clandestine
• experimental
• hidden
• private