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
Removing the Department of Justice’s regulations prohibiting unfair discriminatory policies takes away critical safeguards against the most insidious forms of exclusion.
—
Associate News Editor, MSNBC Newsweek, 10 Dec. 2025
The hysteria about a superior race, the insistence that all would be well if one insidious group was purged—those doctrines had been entirely defeated.
—Joan Silber, New Yorker, 30 Nov. 2025
The difference between that film and Pluribus is that this bold-type message is not as baldly oppressive or insidious.
—Scott Tobias, Vulture, 7 Nov. 2025
In fact, our youngest teens, Generation Alpha—those born between 2010 and 2024—could be at risk of something else insidious.
—Hannah Silverman, Parents, 31 Oct. 2025
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
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Snow, ice and freezing temperatures hit parts of Europe on Tuesday, causing treacherous traffic conditions that left at least five people dead in France and forcing the cancellation of hundreds of flights from one of the continent’s busiest airports.—
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With a combination of rain and snow in the week prior, David Motley, the city’s public relations director, said beach conditions were treacherous.—
Adjective
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With her signature long waves gathered into a subtle bun at the nape of her neck, this style puts the focus on the sculptural wave framing Seyfried's face opposite a deep side part.—
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Grande wore a glossy pink shade on her lips, sculpted cheeks with subtle shimmer, and long lashes.—
Adjective
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Plants that provide winter interest, including sedums, goldenrod, blue false indigo, and ornamental grasses.—
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Today’s teenagers can produce a TikTok video in minutes, but how many of them will learn to analyze the president’s false claim that Tylenol causes autism?—
Adjective
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While not everyone gets their wishes, those with no interest in taking on the deceptive — and challenging — role of a Traitor likely won't be chosen.—
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The legal claims included negligence, wrongful death, deceptive trade practices, and product liability.—
Adjective
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Her Ashley is the movie’s fourth and fifth wheel, dismissed as both a perfidious troublemaker and a New Age airhead—a life coach in need of a wife coach.—
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This perfidious situation, unintentional as its creation may have been, was strongly critiqued as far back as 1983 by Jonathan Crush and Paul Wellings in an article in The Journal of Modern African Studies.—
Adjective
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Everything was really incorrect for the period—shiny, sparkly, overdone—but the actual shapes and silhouettes of his clothes are quite accurate.—
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Avoid harsh or incorrect cleaners and follow manufacturer guidance to protect coatings, airflow, and internal components.—
Adjective
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As analysis, that’s not wrong, but where’s the sting of it inside this bizarre bonbon of a musical?—
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Despite his brilliance and intellect, he was prevented from having a full life by being born on the wrong side of Israel’s separation fence.—
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 12 Jan. 2026.
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