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
Neetika Walter, Interesting Engineering, 8 May 2026
The Delta tunnel project A major focus of the speech was the Delta Conveyance Project, commonly known as the Delta tunnel project, which would reroute water from the Sacramento-San Joaquin River Delta to Southern California through a massive underground tunnel system.
—Richard Ramos, CBS News, 8 May 2026
Jacopo Prisco, CNN Money, 20 Apr. 2026
Those people will add to traffic and congestion on Kansas City’s roads, which is why the city is wrapping up many of its infrastructure projects before June, from an 18th and Vine parking garage to a Westport underground reservoir.
—Eleanor Nash, Kansas City Star, 20 Apr. 2026
Lisa Song, ProPublica, 7 May 2026
However, Daredevil and several of his fellow vigilantes had to go underground in order to expose Kingpin's lies.
—Staff Author, PEOPLE, 6 May 2026
See All Example Sentences for underground
Adjective
Pangea 5 will be used to process complex geological and energy data, including advanced seismic imaging that helps energy companies map underground structures more accurately.
—Neetika Walter, Interesting Engineering, 8 May 2026
The Delta tunnel project A major focus of the speech was the Delta Conveyance Project, commonly known as the Delta tunnel project, which would reroute water from the Sacramento-San Joaquin River Delta to Southern California through a massive underground tunnel system.
—Richard Ramos, CBS News, 8 May 2026
Noun
The European Space Agency’s rover Rosalind Franklin, expected to launch in late 2028 for a landing on Mars in 2030, will explore the northern hemisphere with the ability to probe both the surface and underground.
—Jacopo Prisco, CNN Money, 20 Apr. 2026
Those people will add to traffic and congestion on Kansas City’s roads, which is why the city is wrapping up many of its infrastructure projects before June, from an 18th and Vine parking garage to a Westport underground reservoir.
—Eleanor Nash, Kansas City Star, 20 Apr. 2026
Adverb
That principle is why coal miners once brought canaries underground, as one emergency medicine doctor explained in a recent court declaration.
—Lisa Song, ProPublica, 7 May 2026
However, Daredevil and several of his fellow vigilantes had to go underground in order to expose Kingpin's lies.
—Staff Author, PEOPLE, 6 May 2026
See All Example Sentences for underground
Recent Examples of Synonyms for underground
Adjective
-
Filling out the role of Ilya is Jay Armstrong Johnson; Jimin Moon plays Shane; Ryann Redmond plays a wine-mom narrator who lives for their clandestine love.—
Dan Stahl,
New Yorker,
1 May 2026
-
For those escaping to Philadelphia from regions nearer to Pennsylvania, clandestine travel by small boat or by road was more likely than stowing away on a steamship.—
Jeremy Mennis,
The Conversation,
1 May 2026
Adjective
-
The architecture of the subterranean pathways that funnel magma to the surface, the chemistry of the magma, the cadence of eruptions, and the assortment of eruption styles differ from place to place.—
Quanta Magazine,
Quanta Magazine,
8 May 2026
-
The utility has a subterranean network of some 4,600 miles of pipes under the city, including significant stretches of original cast and ductile iron — some dating back to the 1800s — which pose a risk of gas leaks that could lead to an explosion.—
Robert Channick,
Chicago Tribune,
6 May 2026
Noun
-
Magyar—sitting in the front row, rewatching a film that had helped establish him as a global icon of anti-authoritarian resistance—was less than four days away from taking power.—
Andrew Marantz,
New Yorker,
9 May 2026
-
It was systematically dismantled by the fierce, courageous resistance of Black mothers, soldiers, and civil rights workers who recognized the lethal power of these performances and put everything on the line to change the course of our history.—
Erik Pedersen,
Oc Register,
8 May 2026
Adjective
-
Khatri approached the undercover officer who had just presented the store’s clerk with a fake $1,000 winning ticket, court records show.—
Jack Jankowski,
The Orlando Sentinel,
9 May 2026
-
This image provided by the Justice Department and contained in the affidavit in support of a criminal complaint shows Victor Manuel Rocha during a meeting with a FBI undercover employee.—
Sergio Candido,
CBS News,
8 May 2026
Adverb
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That meant the magma could easily, and stealthily, pry its way through the crust, rather than having to smash through solid rock.—
Robin George Andrews,
Scientific American,
23 Apr. 2026
-
As Adrian Van Young put it in the Southwest Review, the book’s draw is stealthily structural.—
Brittany Allen,
Literary Hub,
23 Apr. 2026
Adjective
-
Lothar Speer During his sentencing in 2024, federal prosecutors said the full damage caused by Rocha's decades-long covert relationship with Cuba may never be fully known.—
Sergio Candido,
CBS News,
8 May 2026
-
Ukraine has also conducted long-range covert drone strikes launched from within Russian territory, including attacks on strategic airbases using drones concealed in trucks or civilian infrastructure, demonstrating the increasing reach of low-cost UAV systems into deep strategic targets.—
Encyclopedia Britannica,
Encyclopedia Britannica,
8 May 2026
Adverb
-
Haslach also admitted to surreptitiously taking a photo of a minor in a swimsuit by positioning his cellphone under a classroom desk.—
Nick Ferraro,
Twin Cities,
1 May 2026
-
Sometimes the batteries on the trackers would run low, and McGovern’s team would need to remove and recharge the devices, before surreptitiously replacing them.—
Ed Caesar,
New Yorker,
30 Apr. 2026
Adjective
-
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 13 May. 2026.
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