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

undergrounds plural

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

Other Word Forms

Noun Inflected Forms

• undergrounds
  plural

Etymology

Origin of underground

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

Example Sentences

Operating at the former Homestake Gold Mine site, the Sanford Underground Research Facility is America’s deepest underground science lab.

From The Wall Street Journal • Jun. 25, 2026

My recitation about the environmental ingenuity of enslaved people in the Underground Railroad was clearly jarring to many in the audience, perhaps even hostile to their understanding of Blackness.

From Salon • Jun. 19, 2026

In 2025, researchers published a global analysis of underground mycorrhizal fungal diversity in Nature and launched a digital platform called the Underground Atlas to help identify likely biodiversity hotspots beneath the surface.

From Science Daily • Jun. 15, 2026

The watchdog said the advert seen on the London Underground stated the mask was "skin tech that's light years ahead" and it expected "robust, product-specific evidence" to support this.

From BBC • Jun. 9, 2026

It was in this office, upstairs in Lebanon Seminary, that she learned the extent of the network of stops on the Underground Railroad.

From "Harriet Tubman: Conductor on the Underground Railroad" by Ann Petry

Related Words

• clandestine
• experimental
• hidden
• private