underground

1 of 3

adverb

un·​der·​ground ˌən-dər-ˈgrau̇nd 

1

: beneath the surface of the earth

2

: in or into hiding or secret operation

underground

2 of 3

noun

ˈən-dər-ˌgrau̇nd 

1

: a subterranean space or channel

2

: an underground city railway system

3

a

: a movement or group organized in strict secrecy among citizens especially in an occupied country for maintaining communications, popular solidarity, and concerted resistive action pending liberation

b

: a clandestine conspiratorial organization set up for revolutionary or other disruptive purposes especially against a civil order

c

: an unofficial, unsanctioned, or illegal but informal movement or group

especially : a usually avant-garde group or movement that functions outside the establishment

underground

3 of 3

adjective

un·​der·​ground ˈən-dər-ˌgrau̇nd 

1

: being, growing, operating, or situated below the surface of the ground

2

: conducted by secret means

3

a

: existing outside the establishment

an underground literary reputation

b

: existing outside the purview of tax collectors or statisticians

the underground economy

4

a

: produced or published outside the establishment especially by the avant-garde

underground movies

underground newspapers

b

: of or relating to the avant-garde underground

an underground moviemaker

an underground theater

Synonyms

Noun

• resistance

Adjective

• backstairs
• behind-the-scenes
• clandestine
• covert
• furtive
• hole-and-corner
• hugger-mugger
• hush-hush
• private
• privy
• secret
• sneak
• sneaking
• sneaky
• stealth
• stealthy
• surreptitious
• undercover
• underhand
• underhanded

Examples of underground in a Sentence

Adverb

They had been living underground as fugitives.

Noun

I've ridden on the New York subway, the Paris Metro, and the London Underground.

joined the underground while still a teenager

Adjective

The drugs are supplied through an underground network.

She loves the city's underground music scene.

Recent Examples on the Web

Adverb

Foundations and underground cables made of concrete, plastic, and metal can usually be recycled but are often left underground when a project is discontinued. —Ariel Cohen, Forbes, 23 Dec. 2024

The study, published in Science Advances, examined microbes from up to 3 miles underground and 1,600 feet beneath the seafloor. —Benedict Cosgrove, Newsweek, 19 Dec. 2024

Noun

An Enbridge Energy pipeline in Jefferson County spilled nearly 70,000 gallons of crude oil underground, according to federal officials. —Drake Bentley, Journal Sentinel, 13 Dec. 2024

Crews arrived to find a partial collapse of the parking lot behind the stores and an active fire underground, according to the press release. —Yaakov Katz, Newsweek, 28 Nov. 2024

Adjective

The Netflix series, written by Joe Barton (the creator of the underrated crime thriller Giri/Haji), is a darkly funny, thrillingly brutal, ludicrously self-aware yarn about underground crime networks, diplomatic crises, and espionage. —Sophie Gilbert, The Atlantic, 24 Dec. 2024

Complete decommissioning can include felling or dismantling the turbines, partially or wholly removing the turbine foundations and underground cables, removing the ground-level facilities, and restoring the land to a usable state. —Ariel Cohen, Forbes, 23 Dec. 2024

Word History

First Known Use

Adverb

14th century, in the meaning defined at sense 1

Noun

1594, in the meaning defined at sense 1

Adjective

1601, in the meaning defined at sense 1

Phrases Containing underground

• go underground
• the underground

Kids Definition

underground

1 of 3 adverb

un·​der·​ground ˌən-dər-ˈgrau̇nd 

1

: below the surface of the ground

an underground passage

2

: in or into hiding or secret operation

the political party went underground

underground

2 of 3 noun

un·​der·​ground

ˈən-dər-ˌgrau̇nd

1

: a space under the surface of the ground

especially : subway sense 2

2

: a secret political group

especially : an organized body working in secret to overthrow a government or an occupying power

underground

3 of 3 adjective

un·​der·​ground ˈən-dər-ˌgrau̇nd 

1

: being, growing, operating, or located below the surface of the ground

an underground stream

2

: conducted secretly