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
Hira Humayun, CNN Money, 22 May 2026
The agency initially reported early Saturday eight people were killed and 38 were trapped underground.
—ABC News, 22 May 2026
Terry Gross, NPR, 18 May 2026
Though many people come to far West Texas for its isolation—the Unabomber’s slightly less reclusive brother did a stint here in the eighties, living at first in a crude underground shelter—Miller said that immigration-enforcement agents have been an intrusive presence for many years.
—Rachel Monroe, New Yorker, 14 May 2026
John Werner, Forbes.com, 24 May 2026
Loud explosions were heard in the Ukrainian capital, causing a residential building near the government district to shake, while dozens took shelter in an underground metro station in the city center, according to Agence France-Presse journalists.
—CBS News, 24 May 2026
See All Example Sentences for underground
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Adverb
At least eight people are dead and 38 others are trapped underground after a gas explosion in a coal mine in northeast China’s Shanxi province on Friday night, according to state media.
—Hira Humayun, CNN Money, 22 May 2026
The agency initially reported early Saturday eight people were killed and 38 were trapped underground.
—ABC News, 22 May 2026
Noun
Zayd Ayers Dohrn spent much of his childhood underground and on the run.
—Terry Gross, NPR, 18 May 2026
Though many people come to far West Texas for its isolation—the Unabomber’s slightly less reclusive brother did a stint here in the eighties, living at first in a crude underground shelter—Miller said that immigration-enforcement agents have been an intrusive presence for many years.
—Rachel Monroe, New Yorker, 14 May 2026
Adjective
The Stata Center is a 430,000-square-foot academic complex with a 290,000-square-foot underground garage, and dates back to 2004.
—John Werner, Forbes.com, 24 May 2026
Loud explosions were heard in the Ukrainian capital, causing a residential building near the government district to shake, while dozens took shelter in an underground metro station in the city center, according to Agence France-Presse journalists.
—CBS News, 24 May 2026
See All Example Sentences for underground
Cite this Entry
“Underground.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/underground. Accessed 27 May. 2026.
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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