underground

[uhn-der-ground, uhn-der-ground]

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

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

Word History and Origins

Origin of underground¹

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

Example Sentences

“You don’t leave until you have 100% mop-up because fire can hide underground and reignite unexpectedly even weeks later,” he said.

Read more on Los Angeles Times

Federal investigators say the Lachman fire was deliberately set and had burned underground in a canyon root system until the winds rekindled it on Jan. 7.

Read more on Los Angeles Times

The temporary suspension of underground operations at Freeport Indonesia following the mid-2025 landslide has disrupted gold supply in Indonesia, the analyst notes.

Read more on The Wall Street Journal

In a bid to circumvent these prohibitions, Bakhtari launched the "Daughters" programme that enables Afghan girls to receive support to study in secret underground schools or online.

Read more on Barron's

With the rat squeaking directions in her ear, Roz stomped deeper into the underground.

Read more on Literature

Related Words

• clandestine 
• experimental 
• hidden 
• private