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
Lauren Liebhaber, Miami Herald, 14 Apr. 2025
Such restrictions only push AI use underground, increasing risk rather than reducing it.
—Cal Al-Dhubaib, Forbes.com, 11 Apr. 2025
Kyle Martin, The Mercury News, 24 Jan. 2025
In the ever-evolving cyber underground, ransomware extortionists have grown to become perhaps the most sophisticated and formidable threat.
—Etay Maor, Forbes.com, 26 Mar. 2025
Alice George, Smithsonian Magazine, 18 Apr. 2025
This week, Lawrence Burney steps in to talk about how a part of Baltimore lingo is entering the wider underground rap lexicon through artists from the Mid-Atlantic.
—Lawrence Burney, Pitchfork, 18 Apr. 2025
See All Example Sentences for underground
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Adverb
The flowerpot blind snake lives primarily underground, feeding exclusively on termites and ants, researchers said.
—Lauren Liebhaber, Miami Herald, 14 Apr. 2025
Such restrictions only push AI use underground, increasing risk rather than reducing it.
—Cal Al-Dhubaib, Forbes.com, 11 Apr. 2025
Noun
The city this month began drilling at Del Prado Park, the first of several sites being explored to find safe, potable water underground.
—Kyle Martin, The Mercury News, 24 Jan. 2025
In the ever-evolving cyber underground, ransomware extortionists have grown to become perhaps the most sophisticated and formidable threat.
—Etay Maor, Forbes.com, 26 Mar. 2025
Adjective
Disco first emerged in underground Black, Latino and gay clubs where people created their own version of dance music.
—Alice George, Smithsonian Magazine, 18 Apr. 2025
This week, Lawrence Burney steps in to talk about how a part of Baltimore lingo is entering the wider underground rap lexicon through artists from the Mid-Atlantic.
—Lawrence Burney, Pitchfork, 18 Apr. 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 22 Apr. 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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