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
Jon Rosemberg, Fortune, 9 Dec. 2025
There’s a scene where the miners are all working underground.
—Literary Hub, 8 Dec. 2025
Jenn Pelly, Time, 4 Dec. 2025
Its suffocating Puritanic culture is suddenly rocked by an exhilarating theater movement fostering the likes of Tamburlaine and Doctor Faustus, but also by an underground of intrigue and dissent that’s hatching schemes to blow up Parliament and extinguish royal rule.
—Peter Bart, Deadline, 4 Dec. 2025
Samantha Stutsman, PEOPLE, 7 Dec. 2025
What To Know The volcano showed low-level activity starting in July 2025, including underground magma movement and early sulfur dioxide emissions, according to the Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), as cited in a NASA report Thursday.
—MSNBC Newsweek, 5 Dec. 2025
See All Example Sentences for underground
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Adverb
These small adjustments, almost invisible at first, can become like roots spreading underground and creating the conditions for something sturdier to grow.
—Jon Rosemberg, Fortune, 9 Dec. 2025
There’s a scene where the miners are all working underground.
—Literary Hub, 8 Dec. 2025
Noun
This ambient folk album from a fixture of the UK underground uses minimalist instrumentation—little more than Roberston’s luminescent voice and brittle acoustic guitar—for maximalist feeling.
—Jenn Pelly, Time, 4 Dec. 2025
Its suffocating Puritanic culture is suddenly rocked by an exhilarating theater movement fostering the likes of Tamburlaine and Doctor Faustus, but also by an underground of intrigue and dissent that’s hatching schemes to blow up Parliament and extinguish royal rule.
—Peter Bart, Deadline, 4 Dec. 2025
Adjective
In season 2, episode 3, several of Tommy’s crew members are exposed to hydrogen sulfide (H₂S) — a toxic gas that can escape from underground reservoirs during oil drilling.
—Samantha Stutsman, PEOPLE, 7 Dec. 2025
What To Know The volcano showed low-level activity starting in July 2025, including underground magma movement and early sulfur dioxide emissions, according to the Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), as cited in a NASA report Thursday.
—MSNBC Newsweek, 5 Dec. 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 14 Dec. 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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