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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Recent Examples of insidious
Hillsides covered in fuel The hills surrounding Concepción, Penco and Lirquén appear deep green from the air, carpeted in trees, and in the thickness of these forests lies an insidious risk.
—
Stefano Pozzebon, CNN Money, 26 Apr. 2026
Public narratives that frame low teen birth rates as a problem will only intensify these insidious efforts by introducing new people to pronatalist beliefs and fostering support for efforts that undermine contraceptive access.
—Riley J. Steiner, STAT, 20 Apr. 2026
After all, offenses committed by individuals in positions of public trust are especially insidious.
—Craig MacLellan, Boston Herald, 3 Apr. 2026
The trailer released this week (below) shows the gang during happier times in 1985 — before the latter seasons would introduce villain Vecna (played by Jamie Campbell Bower in the original series) and an even more insidious era of the Upside Down.
—Jackie Strause, HollywoodReporter, 27 Mar. 2026
See All Example Sentences for insidious
Stefano Pozzebon, CNN Money, 26 Apr. 2026
Public narratives that frame low teen birth rates as a problem will only intensify these insidious efforts by introducing new people to pronatalist beliefs and fostering support for efforts that undermine contraceptive access.
—Riley J. Steiner, STAT, 20 Apr. 2026
After all, offenses committed by individuals in positions of public trust are especially insidious.
—Craig MacLellan, Boston Herald, 3 Apr. 2026
The trailer released this week (below) shows the gang during happier times in 1985 — before the latter seasons would introduce villain Vecna (played by Jamie Campbell Bower in the original series) and an even more insidious era of the Upside Down.
—Jackie Strause, HollywoodReporter, 27 Mar. 2026
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
-
Ships have increasingly traveled through the Panama Canal as shipments are rerouted and buyers purchase from other countries to avoid commerce through now-treacherous Middle Eastern waterway.—
Alma Solis,
Fortune,
24 Apr. 2026
-
Ben hunts, and Sasha tries to survive, not just him but various treacherous and dangerous elements that make that mountain climb at the start look like kids play.—
Pete Hammond,
Deadline,
23 Apr. 2026
Adjective
-
With Pluto turning retrograde in your 12th House of Reflection, patterns, habits, or emotional cycles may come into focus in subtle but meaningful ways.—
Tarot.com,
The Orlando Sentinel,
6 May 2026
-
Now, there’s no mention of Eugenie’s extended family, just a subtle but clear message about their connection to the King and no one else.—
Lizzie Lanuza,
StyleCaster,
6 May 2026
Adjective
-
The boy’s mother, Tommi Jo Mejer, 50, of Aliso Viejo, was arrested days after the accident and charged with child endangerment, accessory after the fact, contributing to the delinquency of a minor and providing false information to a peace officer.—
Fedor Zarkhin,
Los Angeles Times,
1 May 2026
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The boy’s mother, 50-year-old Tommi Jo Mejer of Aliso Viejo, was later arrested and charged with felony child endangerment, being an accessory after the fact and several misdemeanors, including contributing to the delinquency of a minor and providing false information to a peace officer.—
Sydney Barragan,
Oc Register,
1 May 2026
Adjective
-
Charted on an outdated seating map weeks before the official on-sale date, these deceptive listings falsely suggested the performance was almost sold out.—
Lori Dimun,
Chicago Tribune,
6 May 2026
-
There is a broader issue of manufacturers selling dangerous products and promoting them with deceptive advertising to lure youth into using their dangerous, ineffective products.—
Jad Abdel Nour,
Hartford Courant,
4 May 2026
Adjective
-
Pakistan was a perfidious ‘ally’ in Afghanistan, backing the Taliban while pretending to be our friends.—
Efrat Lachter,
FOXNews.com,
18 Apr. 2026
-
The government took a genuine invitation to collaborate as a perfidious power grab.—
Gideon Lewis-Kraus,
New Yorker,
14 Mar. 2026
Adjective
-
The part where there's a problem is the FIFA president spreading incorrect information about ticket prices while standing to benefit a great deal from higher costs.—
Dan Zaksheske OutKick,
FOXNews.com,
6 May 2026
-
Low-quality over-the-counter (OTC) products, incorrect dose, or decreased absorption can be a few reasons.—
Ayesha Gulzar,
Verywell Health,
6 May 2026
Adjective
-
Wallace and her collaborators scrambled to get into the water; the whale was swimming in the wrong direction, toward some docks.—
Jessica Camille Aguirre,
New Yorker,
2 May 2026
-
What most people get wrong is conflating the theme of the exhibition with the dress code for the evening.—
José Criales-Unzueta,
Vanity Fair,
2 May 2026
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 8 May. 2026.
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