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

The first phase of the D Line extension, opening Friday, will offer just 3.92 miles of new subway along Wilshire with three new underground stations at La Brea, Fairfax and La Cienega.

From Los Angeles Times • May 7, 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

Those conversations gradually expanded into exploring whether the same underground spaces could support other energy uses.

From Science Daily • May 6, 2026

And excavated deep beneath the surface, where the soil allowed, were shell-proof underground shelters, or dugouts in places thirty or more feet deep, approached down wooden staircases.

From "The War to End All Wars: World War I" by Russell Freedman

Related Words

• clandestine
• experimental
• hidden
• private