underground

American  

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

adverb

1. beneath the surface of the ground: ground.

   traveling underground by subway.

2. in concealment or secrecy; not openly.

   subversion carried on underground.

---

adjective

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

---

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

Then it would need to be mechanically excavated from deep underground in the middle of hostile territory and could weigh 1,000 pounds.

From Salon • Apr. 3, 2026

Kone does much of its research underground in Lohja, Finland, in a facility sunk deep into a working limestone mine that lets engineers test travel distances of more than three football fields.

From The Wall Street Journal • Apr. 2, 2026

In the lowland areas that include Los Angeles, rattlesnakes have underground burrows that are home to one or maybe two snakes, Taylor said.

From Los Angeles Times • Apr. 1, 2026

Then there is Qeshm, the largest island in the Gulf and 75 times bigger than Kharg, where Iran is suspected of housing underground missile and drone sites.

From BBC • Mar. 30, 2026

The map showed clearly that they must begin their climb at the place where the water gushed from its underground tunnel to form the stream.

From "Rowan of Rin" by Emily Rodda

Related Words

• clandestine
• experimental
• hidden
• private