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
Synonyms
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
Brandee Gruener, Southern Living, 28 Jan. 2025
To explore this, Dundas and his team ran models based on flood volumes and flow rates that could occur if water were trapped deep underground.
—Victoria Corless, Space.com, 24 Jan. 2025
Rania Aniftos, Billboard, 16 Jan. 2025
And as surface temperatures rise, their cool underground burrows may become important refuges.
—Sammy Roth, Los Angeles Times, 7 Jan. 2025
Lily Ford, The Hollywood Reporter, 5 Feb. 2025
In Spring, a brutal Immigration Removal Centre is described in distressing detail—but Smith also imagines a kind of underground railroad for migrants anxious to avoid the authorities.
—Adam Begley, The Atlantic, 4 Feb. 2025
See all Example Sentences for underground 
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Adverb
Geothermal heat pumps work by pushing heat underground or pulling it from underground, depending on the season.
—Brandee Gruener, Southern Living, 28 Jan. 2025
To explore this, Dundas and his team ran models based on flood volumes and flow rates that could occur if water were trapped deep underground.
—Victoria Corless, Space.com, 24 Jan. 2025
Noun
His breakthrough came via 1977’s Eraserhead, which became popular in the midnight movie underground circuit.
—Rania Aniftos, Billboard, 16 Jan. 2025
And as surface temperatures rise, their cool underground burrows may become important refuges.
—Sammy Roth, Los Angeles Times, 7 Jan. 2025
Adjective
It was called a hypothesis on how to perfectly construct an underground civilization built for 25,000 people.
—Lily Ford, The Hollywood Reporter, 5 Feb. 2025
In Spring, a brutal Immigration Removal Centre is described in distressing detail—but Smith also imagines a kind of underground railroad for migrants anxious to avoid the authorities.
—Adam Begley, The Atlantic, 4 Feb. 2025
See all Example Sentences for underground
Dictionary Entries Near underground
Cite this Entry
“Underground.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/underground. Accessed 8 Feb. 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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