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

Ukrainian artwork and drone carcasses provide an eclectic decor to the interior of Brovdi's underground bunker, from where he commands a unified force of some of Ukraine's highest-ranking drone units.

From Barron's • Jun. 10, 2026

Also included are the sites of underground gas storage facilities, refineries, fuel terminals, legacy pollution sites, active industrial sites, landfills, dumps and recycling centers.

From Los Angeles Times • Jun. 6, 2026

When he’s working on a new movie, she says, “he’ll ‘Beautiful Mind’ it, these weird Post-its everywhere, and then he’ll go underground for a week and write a near-perfect draft.”

From The Wall Street Journal • Jun. 4, 2026

According to a CNN report on Sunday, satellite images show that Iran has unblocked 50 out of the 69 tunnel entrances bombed by the US and Israel at 18 underground missile facilities.

From Barron's • Jun. 4, 2026

More and more, I was leaving the watch shop to her and Father as our underground “operation” required more time.

From "The Hiding Place" by Corrie ten Boom

Related Words

• clandestine
• experimental
• hidden
• private