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
JSTOR Daily, 20 Oct. 2025
Then a rental company pointed him to a seven-story chalet built into the side of a mountain in Deer Valley, with five of the floors underground.
—Abby Montanez, Robb Report, 19 Oct. 2025
Winston Cho, HollywoodReporter, 27 Oct. 2025
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
David Garrick, San Diego Union-Tribune, 26 Oct. 2025
Chicago art scene — both eager to claim a place in the thriving underground scene.
—Nora Dahlia, PEOPLE, 25 Oct. 2025
See All Example Sentences for underground
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Adverb
The Tunnels story is that Chinese immigrants built a network of tunnels under the city because they were forced to live underground; the tunnels were then used by gangsters and bootleggers, including Al Capone.
—JSTOR Daily, 20 Oct. 2025
Then a rental company pointed him to a seven-story chalet built into the side of a mountain in Deer Valley, with five of the floors underground.
—Abby Montanez, Robb Report, 19 Oct. 2025
Noun
Ascending from the horror underground, CBS daytime show The Talk covered theater-goers hurling at screenings.
—Winston Cho, HollywoodReporter, 27 Oct. 2025
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
Adjective
That change is possible because California recently loosened its purification rules to allow purified wastewater to be pumped directly into a water system, instead of being stored for months in reservoirs or underground basins.
—David Garrick, San Diego Union-Tribune, 26 Oct. 2025
Chicago art scene — both eager to claim a place in the thriving underground scene.
—Nora Dahlia, PEOPLE, 25 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 29 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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