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

If there were a statewide measure for commercial businesses, many would probably have to build retention ponds or swales to filter out contaminants before water percolates underground.

From Los Angeles Times • Jun. 5, 2026

During a recent tour of the ballroom site for reporters, Trump said it would feature underground meeting rooms, a military hospital and a "drone-proof" roof.

From Barron's • Jun. 5, 2026

Tragedy struck in 1972 when fire broke out deep underground and 91 miners died.

From The Wall Street Journal • Jun. 4, 2026

We were two floors underground, and yet we could feel and hear the massive explosions above.

From BBC • Jun. 2, 2026

Paris explained that the trip would take three to four hours, and because there was no cellular service underground, there’d be no way to communicate with the world above.

From "City Spies" by James Ponti

Related Words

• clandestine
• experimental
• hidden
• private