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

Adapting to them often means having to move life underground. —Patrick Reevell, ABC News, 21 June 2024

The men’s bodies were later found 14 feet underground at the Neshoba County farm on August 4. —Emily Palmer, Peoplemag, 21 June 2024

Noun

The package includes funding to help build a 1,300 space underground garage, which will open up land just east Billy Bob’s Texas and north of East Exchange Street. —Harrison Mantas, Fort Worth Star-Telegram, 25 June 2024

The company also highlighted that the mine’s power supply will come from renewable energy with a future all-electric underground mining fleet. —Sarah Lapidus, The Arizona Republic, 22 May 2024

Adjective

Large-capacity cesspools — which serve 20 or more people per day — release untreated sewage, which can contaminate underground sources of drinking water with pathogens, according to the EPA. —Lila Seidman, Los Angeles Times, 30 June 2024

According to Stantec, an engineering and architecture company, the $25 million project included a new underground water vault to collect storm water and reduce flooding. —Hanh Truong, Sacramento Bee, 29 June 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