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
Nicole Fallert, USA Today, 26 June 2025
The amount of groundwater replenishment during the 2024 water year, while significant, was less than the 8.7 million acre-feet that percolated underground during the extremely wet 2023 water year, according to state estimates.
—Ian James, Los Angeles Times, 24 June 2025
David Bressan, Forbes.com, 19 June 2025
New York is home to a thriving underground of edgy, experimental noise bands right now, and Brutus VIII, the conceptual project led by musician Jackson Katz, is one of the best.
—Simon Vozick-Levinson, Rolling Stone, 6 May 2025
Natalie Melzer, Chicago Tribune, 17 June 2025
On June 13, Iran confirmed that Israel hit the Natanz nuclear facility, the country's main underground multi-level enrichment site.
—Amira El-Fekki, MSNBC Newsweek, 16 June 2025
See All Example Sentences for underground
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Adverb
Early evidence has shown the bombing did not reach depths necessary to destroy the facilities, which are buried deeply underground, according to a second U.S. official.
—Nicole Fallert, USA Today, 26 June 2025
The amount of groundwater replenishment during the 2024 water year, while significant, was less than the 8.7 million acre-feet that percolated underground during the extremely wet 2023 water year, according to state estimates.
—Ian James, Los Angeles Times, 24 June 2025
Noun
Turkmenistan possesses the world’s fourth largest reserves of natural gas in its underground, exporting gas to countries such as Pakistan, China, India, Iran and Russia.
—David Bressan, Forbes.com, 19 June 2025
New York is home to a thriving underground of edgy, experimental noise bands right now, and Brutus VIII, the conceptual project led by musician Jackson Katz, is one of the best.
—Simon Vozick-Levinson, Rolling Stone, 6 May 2025
Adjective
Israel has struck Natanz repeatedly and claims to have hurt its underground facilities, which experts assess contain 10,000 centrifuges that enrich uranium up to 60%.
—Natalie Melzer, Chicago Tribune, 17 June 2025
On June 13, Iran confirmed that Israel hit the Natanz nuclear facility, the country's main underground multi-level enrichment site.
—Amira El-Fekki, MSNBC Newsweek, 16 June 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 1 Jul. 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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