un·der·ground
ˌən-dər-ˈgrau̇nd 
1
: beneath the surface of the earth
2
: in or into hiding or secret operation
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
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
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
Camila Domonoske, NPR, 8 July 2025
The tax credit was designed to support nascent technology that captures carbon emissions and stores them underground.
—Spencer Kimball, CNBC, 3 July 2025
ABC News, 15 June 2025
Turkmenistan possesses the world’s fourth largest reserves of natural gas in its underground, exporting gas to countries such as Pakistan, China, India, Iran and Russia.
—David Bressan, Forbes.com, 19 June 2025
F.k. Plous, Chicago Tribune, 11 July 2025
There are several places to park for Scottsdale Canal Convergence:
Scottsdale Waterfront underground parking garage, 7135 E. Camelback Road.
—Meredith G. White, AZCentral.com, 10 July 2025
See All Example Sentences for underground
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show current usage.
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Adverb
The chemicals that leach up from deep underground, including benzene and arsenic, can harm human health and leach into water reservoirs.
—Camila Domonoske, NPR, 8 July 2025
The tax credit was designed to support nascent technology that captures carbon emissions and stores them underground.
—Spencer Kimball, CNBC, 3 July 2025
Noun
But, of course, a facility like Fordow underground is dependent on a lot of infrastructure.
—ABC News, 15 June 2025
Turkmenistan possesses the world’s fourth largest reserves of natural gas in its underground, exporting gas to countries such as Pakistan, China, India, Iran and Russia.
—David Bressan, Forbes.com, 19 June 2025
Adjective
As originally proposed, the CTA Super Loop running west from North and Clybourn would have merely grazed Lincoln Yards with an underground station at the far southwestern corner of the tract, North and Elston.
—F.k. Plous, Chicago Tribune, 11 July 2025
There are several places to park for Scottsdale Canal Convergence:
Scottsdale Waterfront underground parking garage, 7135 E. Camelback Road.
—Meredith G. White, AZCentral.com, 10 July 2025
See All Example Sentences for underground
Cite this Entry
“Underground.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/underground. Accessed 18 Jul. 2025.
Copy CitationKids 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
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