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
Kenna Hughes-Castleberry, Space.com, 14 Oct. 2025
With ideal geology for storing CO₂ underground safely and effectively, the Government of Manitoba passed legislation in 2024 to allow for CO₂ storage.
—Prabhat Ranjan Mishra, Interesting Engineering, 10 Oct. 2025
Benjamin Nathans
september 24, Literary Hub, 24 Sep. 2025
Burnham Yard also is near an Environmental Protection Agency Superfund site for radium contamination, but the Terracon report did not find any indication that there is a substantial amount of radioactive material underground.
—Elliott Wenzler, Denver Post, 14 Sep. 2025
Robert F. Worth, The Atlantic, 19 Oct. 2025
Elliot is recruited by the mysterious leader of an underground group of hackers (played by Slater) to join their organization.
—Raven Brunner, PEOPLE, 19 Oct. 2025
See All Example Sentences for underground
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Adverb
Many parallels exist between being high above the Earth and deep underground.
—Kenna Hughes-Castleberry, Space.com, 14 Oct. 2025
With ideal geology for storing CO₂ underground safely and effectively, the Government of Manitoba passed legislation in 2024 to allow for CO₂ storage.
—Prabhat Ranjan Mishra, Interesting Engineering, 10 Oct. 2025
Noun
Unlike the neo-Leninist underground, moreover, dissidents had no desire to revive Bolshevik revolutionary traditions, with their ideological discipline, armed conspiracy, and noms de guerre.
—Benjamin Nathans
september 24, Literary Hub, 24 Sep. 2025
Burnham Yard also is near an Environmental Protection Agency Superfund site for radium contamination, but the Terracon report did not find any indication that there is a substantial amount of radioactive material underground.
—Elliott Wenzler, Denver Post, 14 Sep. 2025
Adjective
Even underground facilities are usually impossible to build in these places, because the construction sites get targeted.
—Robert F. Worth, The Atlantic, 19 Oct. 2025
Elliot is recruited by the mysterious leader of an underground group of hackers (played by Slater) to join their organization.
—Raven Brunner, PEOPLE, 19 Oct. 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 20 Oct. 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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