1
as in clandestine
undertaken or done so as to escape being observed or known by others
an underground operation to smuggle ancient artifacts out of the country
Synonyms & Similar Words
Relevance
Antonyms & Near Antonyms
2
as in subterranean
being, situated, or operating beneath the surface of the earth
an underground shopping mall that is part of the city's subway system
Synonyms & Similar Words
Antonyms & Near Antonyms
as in resistance
a secret organization in a conquered country fighting against enemy forces
joined the underground while still a teenager
Synonyms & Similar Words
as in undercover
Related Words
Dissimilar Words
Example Sentences
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Recent Examples of underground
Robert A. Cronkleton, Kansas City Star, 12 June 2026
And that’s only the beginning—Santa Rosa is also home to seven natural swimming holes connected via underground caverns, including the 81-foot-deep Blue Hole, a favorite of scuba divers.
—Stacey Leasca, Travel + Leisure, 12 June 2026
Terry Gross, NPR, 18 May 2026
Though many people come to far West Texas for its isolation—the Unabomber’s slightly less reclusive brother did a stint here in the eighties, living at first in a crude underground shelter—Miller said that immigration-enforcement agents have been an intrusive presence for many years.
—Rachel Monroe, New Yorker, 14 May 2026
Literary Hub, 3 June 2026
The wells would extend roughly five miles underground, stretching beneath parts of Erie.
—Sarah Horbacewicz, CBS News, 3 June 2026
See All Example Sentences for underground
Adjective
About two dozen people were treated after firefighters responded to reports of an unconscious person in the SubTropolis underground business complex in Kansas City’s Northland.
—Robert A. Cronkleton, Kansas City Star, 12 June 2026
And that’s only the beginning—Santa Rosa is also home to seven natural swimming holes connected via underground caverns, including the 81-foot-deep Blue Hole, a favorite of scuba divers.
—Stacey Leasca, Travel + Leisure, 12 June 2026
Noun
Zayd Ayers Dohrn spent much of his childhood underground and on the run.
—Terry Gross, NPR, 18 May 2026
Though many people come to far West Texas for its isolation—the Unabomber’s slightly less reclusive brother did a stint here in the eighties, living at first in a crude underground shelter—Miller said that immigration-enforcement agents have been an intrusive presence for many years.
—Rachel Monroe, New Yorker, 14 May 2026
Adverb
Below them, clattering on a dozen parallel tracks, the trains were coming and going, arriving and departing, thundering underground.
—Literary Hub, 3 June 2026
The wells would extend roughly five miles underground, stretching beneath parts of Erie.
—Sarah Horbacewicz, CBS News, 3 June 2026
See All Example Sentences for underground
Recent Examples of Synonyms for underground
Adjective
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Some may be announced publicly; others may happen in more clandestine ways.—
Eben Novy-Williams,
Sportico.com,
10 June 2026
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But clandestine flows aren’t the biggest factor behind the market calm.—
Matt Egan,
CNN Money,
9 June 2026
Adjective
-
The Spa My first visit to the hotel's subterranean spa was nearly a decade ago.—
Lane Nieset,
Travel + Leisure,
12 June 2026
-
Guests and a small community of local members enter a subterranean sanctuary of saunas, steam rooms, rain showers, a hydrotherapy pool, and serene treatment suites offering everything from exosome facials and pelvic-floor toning therapy to detox IV drips.—
Condé Nast,
Condé Nast Traveler,
10 June 2026
Noun
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This longer, more persistent form of CAR-T cell therapy can help prevent tumors from developing resistance against them.—
Charles J. Dimitroff,
The Conversation,
12 June 2026
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Dems slow to embrace data center resistance McMillan Cottom suggested that no public officials on the right or the left have perfected their messaging to align with anti-data center sentiments.—
Ashley Belanger,
ArsTechnica,
12 June 2026
Adverb
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The building is stealthily spacious with 40 bedrooms, and there’s a serious Sisley spa, designed with monkish minimalism, plus four superb restaurants.—
Matt Ortile,
Condé Nast Traveler,
3 June 2026
-
The strategic insights that matter most—how to respond to a competitive threat, whether an acquisition makes sense, how to restructure around AI, and which leadership gaps are stealthily costing the company—are only partly products of rigorous thinking.—
Julian Hayes II,
Forbes.com,
27 May 2026
Adjective
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His most recent conviction resulted from a 2018 case when authorities said he was shot after ramming multiple Fremont undercover police cars, as officers tried to arrest him in a string of car burglaries across the Bay Area.—
Harry Harris,
Mercury News,
8 June 2026
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Years earlier, in 2001, the undercover detective involved claimed her career had been ruined by the case, and received around $166,000 in an out-of-court settlement, per the BBC.—
Caroline Blair,
PEOPLE,
7 June 2026
Adverb
-
As a group of dancers surrounded her on the B-stage, she was surreptitiously harnessed into a rig that carried her aloft, limp yet belting, into the heavens, or at least into what looked like a UFO hovering over the arena.—
Chris Willman,
Variety,
7 June 2026
-
Gray-hat hackers, unlike white-hats, surreptitiously sneak into corporate systems to find security vulnerabilities.—
Winston Cho,
HollywoodReporter,
4 June 2026
Adjective
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The film follows cybersecurity expert Daniel Kellner (Josh O’Connor), who lifts secret files about the existence of aliens from Wardex, a covert non-government organization that used to employ him.—
Tim Lammers,
Forbes.com,
13 June 2026
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The investigation also linked the activity to China based on IP addresses associated with a LinkedIn account and a Gmail account tied to the covert recruitment scheme.—
Michael Kan,
PC Magazine,
10 June 2026
Adverb
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Other examples of politically motivated pirate radio can be found around the world, some of them clandestinely backed by governmental intelligence agencies, but many of them existing as truly grassroots endeavors.—
Encyclopedia Britannica,
Encyclopedia Britannica,
23 Apr. 2026
-
The audio recordings, shared by outlets including VSquare, Frontstory, Delfi Estonia, the Insider, and the Investigative Centre of Jan Kuciak, seem to have been clandestinely gathered.—
Timothy Nerozzi,
The Washington Examiner,
8 Apr. 2026
Cite this Entry
“Underground.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/underground. Accessed 15 Jun. 2026.
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