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 of underground

Noun

• resistance

Adjective

• clandestine
• undercover
• covert
• sneak
• private

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

Hardware undergoes extensive testing before moving underground Ensuring the reliability of every line-replaceable unit (LRU) has been a key focus throughout the Scorpius project. — Bojan Stojkovski, Interesting Engineering, 26 July 2026

There are about 547 miles of trunk line underground across the city and 6,780 miles of distribution pipes, or main lines, in Los Angeles. — Hannah Fry, Los Angeles Times, 25 July 2026

Noun

Head underground The Bee’s diversions reporter Camila Pedrosa recently ventured deep into the earth, twice, to explore Black Chasm Cavern in Amador County, as well as California Cavern in Calaveras County. — Anne Ewbank, Sacbee.com, 1 Aug. 2026

Her work has included uncovering human trafficking networks, revealing an ISIS underground torture prison in Syria, documenting the war in Ukraine and interviewing senior political figures and world leaders. — Efrat Lachter, FOXNews.com, 30 July 2026

Adjective

These were voices—complaining, confiding, exasperated, distressed—that had not been heard before, as if the novel were a speaking tube cued to an underground rumble. — Cynthia Zarin, Harpers Magazine, 4 Aug. 2026

Eden Aurelius is a relatively recent arrival to New York’s underground club scene, but her slim discography so far shows remarkable focus. — Philip Sherburne, Pitchfork, 4 Aug. 2026

Word History

First Known Use

Adverb

1598, 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

Rhymes for underground

• aboveground
• battleground
• belowground
• paperbound
• turnaround
• ultrasound
• wraparound
• abound
• aground
• around
• astound
• background

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