as in treacherous
formal
causing harm in a way that is gradual or not easily noticed
Most people with this insidious disease have no idea that they are infected. an insidious enemy
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Example Sentences
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Recent Examples of insidious
Months later, scientists discovered something far more insidious: The volcano had caused an unexpected seismic reaction that released hazardous levels of CO2 – once trapped in the ground – into the air.
—
Colette Davidson, Christian Science Monitor, 14 Apr. 2025
But beyond this damage lies something more insidious: democratic backsliding.
—Nicholas Creel, MSNBC Newsweek, 5 May 2025
Some marriages don’t unravel through conflict — they get caught in a more insidious, exhausting loop.
—Mark Travers, Forbes.com, 4 May 2025
In humans, the infection is insidious, with an asymptomatic incubation period of between 5 and 15 years.
—ArsTechnica, 23 Apr. 2025
See All Example Sentences for insidious
Colette Davidson, Christian Science Monitor, 14 Apr. 2025
But beyond this damage lies something more insidious: democratic backsliding.
—Nicholas Creel, MSNBC Newsweek, 5 May 2025
Some marriages don’t unravel through conflict — they get caught in a more insidious, exhausting loop.
—Mark Travers, Forbes.com, 4 May 2025
In humans, the infection is insidious, with an asymptomatic incubation period of between 5 and 15 years.
—ArsTechnica, 23 Apr. 2025
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
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Hickey made three trips back and forth in the treacherous water to save the boaters one by one.—
Nicholas Williams,
New York Daily News,
25 May 2025
-
Mastering wet roads: Safety tips for heavy rainfall When heavy rain pours, the risk of flooding and treacherous roads rises.—
Southern California Weather Report,
Oc Register,
24 May 2025
Adjective
-
Arthritis in your fingers often starts with subtle changes.—
Brandi Jones,
Health,
25 May 2025
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The navy, white, and subtle red palette nods to the seaside and seamlessly blends into Printemps' signature French elegance.—
Roxanne Robinson,
Forbes.com,
25 May 2025
Adjective
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The couple was convicted in 2022 of conspiring to defraud banks out of more than $30 million in loans by submitting false documents.—
Eric Tucker,
Chicago Tribune,
30 May 2025
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His career was on a steady rise until a series of accusations and investigations in the mid-2000s — including tax evasion, fraud and making false statements — landed him in prison.—
Rachel Raposas,
People.com,
30 May 2025
Adjective
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The quest to build human-level AI agents using techniques known to produce deceptive tendencies, Bengio says, is comparable to a car speeding down a narrow mountain road, with steep cliffs on either side, and thick fog obscuring the path ahead.—
Harry Booth,
Time,
3 June 2025
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Last year, the Biden administration's Transportation Department opened an inquiry ordering American, Delta Air Lines, Southwest and United to provide records and submit reports to ensure consumers do not face unfair, deceptive, or anticompetitive practices.—
David Shepardson,
USA Today,
3 June 2025
Adjective
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Jake Gyllenhaal is his foil as the perfidious Iago, who goads Othello into unreasoning jealousy with lies about his beloved Desdemona (Molly Osborne).—
New York Times,
New York Times,
17 Feb. 2025
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Since then, Putin has sought instead to rally the public to the defense of a motherland besieged by the perfidious and cunning West.—
Leon Aron,
The Atlantic,
5 Dec. 2024
Adjective
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The senators are incorrect three times, and surely more.—
John Tamny,
Forbes.com,
2 June 2025
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But here’s the twist: both might technically be incorrect.—
Simon Perry,
People.com,
27 May 2025
Adjective
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For affluent Latino parents Enrique and Ilana Gomez, this moment goes hilariously wrong from the start, when their daughter Yoli invites her Mexican-born intended Marcos over to the family’s Pasadena home for dinner.—
Pam Kragen,
San Diego Union-Tribune,
30 May 2025
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There’s a right way and a wrong way to do it Matt Sekerke is a managing director at SEDA Experts and senior macro advisor at Hiddenite Capital Partners.—
Matt Sekerke,
Fortune,
30 May 2025
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 6 Jun. 2025.
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