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
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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
Condé Nast, Condé Nast Traveler, 3 Apr. 2026
Exhibitors include Nicola Bulgari, who keeps part of his vast car collection in an underground garage in central Rome, and sponsors include Swiss bank UBS, Gulfstream, Richard Mille, and RM Sotheby’s.
—Ben Oliver, Robb Report, 3 Apr. 2026
Rupendra Brahambhatt, Interesting Engineering, 22 Feb. 2026
While the concept of finding naturally occurring stores of hydrogen underground is relatively new, Johnson said the process of drilling and producing hydrogen wells is well established science and uses the same rigs used to drill for natural gas.
—Cami Koons, Iowa Capital Dispatch, 17 Feb. 2026
Christopher Bonanos, Curbed, 25 Mar. 2026
Natural gas is a fossil-fuel energy source extracted from deep underground where organic matter, under immense pressure and heat, turns into methane and other gases over millions of years.
—Stephanie Pappas, Scientific American, 23 Mar. 2026
See All Example Sentences for underground
Adjective
The spa The 57-foot-long underground pool is a treasure.
—Condé Nast, Condé Nast Traveler, 3 Apr. 2026
Exhibitors include Nicola Bulgari, who keeps part of his vast car collection in an underground garage in central Rome, and sponsors include Swiss bank UBS, Gulfstream, Richard Mille, and RM Sotheby’s.
—Ben Oliver, Robb Report, 3 Apr. 2026
Noun
Engineers inject water to dissolve part of the salt, pump out the salty brine, and are left with an empty chamber underground.
—Rupendra Brahambhatt, Interesting Engineering, 22 Feb. 2026
While the concept of finding naturally occurring stores of hydrogen underground is relatively new, Johnson said the process of drilling and producing hydrogen wells is well established science and uses the same rigs used to drill for natural gas.
—Cami Koons, Iowa Capital Dispatch, 17 Feb. 2026
Adverb
Although most stations are now wired so mobile phones can be used underground, the signal is often much weaker and the data throughput slower than above.
—Christopher Bonanos, Curbed, 25 Mar. 2026
Natural gas is a fossil-fuel energy source extracted from deep underground where organic matter, under immense pressure and heat, turns into methane and other gases over millions of years.
—Stephanie Pappas, Scientific American, 23 Mar. 2026
See All Example Sentences for underground
Recent Examples of Synonyms for underground
Adjective
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Emergency passports handed off at clandestine locations.—
Shannon K. Kingston,
ABC News,
30 Mar. 2026
-
Jerkins’ family operation included his cousin, Robert Smith, known as Big Bert, with whom Brandy began a clandestine relationship as the recording progressed.—
Jackson Howard,
Pitchfork,
29 Mar. 2026
Adjective
-
The subterranean lower level is dedicated to rest and relaxation.—
Tori Latham,
Robb Report,
2 Apr. 2026
-
Exploring cities like Rome, Madrid, and Athens now means walking through shaded canyons and subterranean malls that feel like airport terminals.—
Big Think,
Big Think,
31 Mar. 2026
Noun
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This approach had a lasting impact, and even centuries after the mainline Crusades to the Holy Land ended, the pope continued to invoke the concept of holy war to justify resistance against the Ottoman Empire and other Muslim entities.—
Brady Knox,
The Washington Examiner,
3 Apr. 2026
-
That would involve changing some state laws, persuading housing lenders to be more accommodating and overcoming resistance from construction unions.—
Dan Walters,
Mercury News,
3 Apr. 2026
Adjective
-
Some of the ammunition was purchased from co-conspirators by undercover officers, prosecutors said.—
Sierra van der Brug,
Oc Register,
31 Mar. 2026
-
Working with a different undercover officer, this time in a European city, Chalker successfully extracted Bernadine to America.—
David D. Kirkpatrick,
New Yorker,
30 Mar. 2026
Adverb
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Such cerebral, stealthily political dramas have made Petzold an auteur’s auteur, beloved by the likes of Claire Denis and Brady Corbet.—
Holden Seidlitz,
New Yorker,
20 Mar. 2026
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But the major platform of the Oscars also brings another level of exposition, which is not always beneficial for a documentary director trying to move stealthily and precisely.—
Rafa Sales Ross,
Variety,
20 Mar. 2026
Adjective
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That secret, a CNN investigation has found, centered on China’s covert plans to massively expand its nuclear ambitions.—
Tamara Qiblawi,
CNN Money,
1 Apr. 2026
-
Movies set in the world of top-secret spycraft and covert operations have entertained audiences for decades.—
Kevin Jacobsen,
Entertainment Weekly,
31 Mar. 2026
Adverb
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Church members would pass them out surreptitiously for evangelism to prospective Iranian converts.—
Angie Leventis Lourgos,
Chicago Tribune,
4 Apr. 2026
-
Maritime tracking firm Winward suggested the ship may have spoofed its location and surreptitiously delivered the fuel to Cuba already.—
Nora Gámez Torres,
Miami Herald,
20 Mar. 2026
Adjective
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Get Ready: Katy Perry Has Released a Sneak Peek of Her New Song And the internet has receipts.—
Mehera Bonner,
Marie Claire,
15 Mar. 2017
Cite this Entry
“Underground.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/underground. Accessed 5 Apr. 2026.
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