insidious

adjective
in·​sid·​i·​ous | \ in-ˈsi-dē-əs How to pronounce insidious (audio) \

Definition of insidious

1a : having a gradual and cumulative effect : subtle the insidious pressures of modern life
b of a disease : developing so gradually as to be well established before becoming apparent
2a : awaiting a chance to entrap : treacherous
b : harmful but enticing : seductive insidious drugs

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Other Words from insidious

insidiously adverb
insidiousness noun

insidious, sinister, or pernicious?

Few would choose to be associated with people or things that are insidious, sinister, or pernicious; all three of these words have decidedly unpleasant meanings, each with its own particular shade of nastiness.

Insidious comes from a Latin word for “ambush” (insidiae), which is fitting, as this word often carries the meanings “deceitful,” “stealthy,” or “harmful in an imperceptible fashion.” The first two meanings may be applied to people or things (“an insidious enemy,” “an insidious plot”), while the last is usually applied to things (“insidious problems,” “insidious sexism”), in particular to the gradual progress of a disease (“an insidious malignancy”).

Sinister comes from a Latin word meaning “on the left side, unlucky, inauspicious.” Although it is commonly used today in the sense “evil” (“a sinister cult leader”; “a sinister plot”), it may also suggest an ominous foreshadowing of some unfavorable turn of events (“a sinister omen”).

Pernicious has largely stayed true to its etymological root, the Latin noun pernicies “ruin, destruction.” Its original meaning in English, “highly injurious or destructive,” usually applies to things (“pernicious apathy,” “pernicious effects”) and medical conditions (“pernicious fever,” “pernicious anemia”). When applied to people, pernicious means “wicked.”

Examples of insidious in a Sentence

But the litigation is also prompting a subtle and insidious change in the way that medicine is practiced, which affects anyone who consults a health professional, even if they would not dream of setting foot in a lawyer's office. It is known as "defensive medicine." — Geoff Watts, New Scientist, 23–29 Oct. 2004 Spin is sometimes dismissed as a simple euphemism for lying. But it's actually something more insidious: indifference to the truth. — Michael Kinsley, Time, 25 Dec. 2000–1 Jan. 2001 As these boats aged and bedding compounds deteriorated, the water torture began, which led to rot, corrosion, and other insidious problems. — Ralph Naranjo, Cruising World, April 1999 Most people with this insidious disease have no idea that they are infected.
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Recent Examples on the Web Especially now, at this sensitive juncture, when the overseers of public spaces are trying to build back trust and operate without risk of spreading this insidious, calamitous infection. Washington Post, "I wondered what it would be like to be vaccinated and back in a theater. My panic lifted as soon as the lights went down.," 7 Apr. 2021 This represents a relatively easy fix to a deeply insidious problem. Rebecca Dixon For Cnn Business Perspectives, CNN, "Black women delivered for Biden. Now it's time for Congress to deliver on a $15 minimum wage," 6 Apr. 2021 The established, false metrics of self-worth are insidious and serpentine. Sophie Gilbert, The Atlantic, "The Unending Assaults on Girlhood," 30 Mar. 2021 But this time, as one of the most racist and insidious laws ever created in this country was passed, the leagues slept. Mike Freeman, USA TODAY, "Opinion: 'We lost:' This time when fighting racism, the sports world failed," 29 Mar. 2021 But there is also a deeper, more insidious side to our eagerness to claim burnout. Jonathan Malesic, The New Republic, "The Exaggeration of “Burnout” in America," 25 Mar. 2021 News of this insidious scheme has raised questions about the fundamental resilience of American democracy—and the thing with the Kremlin is pretty bad too. Andy Greenberg, Wired, "Security News This Week: Homecoming Queen (and Her Mom) Arrested for Alleged Vote Hacking," 20 Mar. 2021 But that does not make the anti-Asian hate speech online less insidious. New York Times, "How Anti-Asian Activity Online Set the Stage for Real-World Violence," 19 Mar. 2021 Among the most insidious claims is that people won’t return to cities for years, if ever. Peter Kern, Fortune, "If you think COVID is the end of cities, you’re wrong," 15 Mar. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'insidious.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of insidious

1545, in the meaning defined at sense 2a

History and Etymology for insidious

Latin insidiosus, from insidiae ambush, from insidēre to sit in, sit on, from in- + sedēre to sit — more at sit

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Time Traveler for insidious

Time Traveler

The first known use of insidious was in 1545

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Last Updated

12 Apr 2021

Cite this Entry

“Insidious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/insidious. Accessed 17 Apr. 2021.

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More Definitions for insidious

insidious

adjective

English Language Learners Definition of insidious

formal : causing harm in a way that is gradual or not easily noticed

insidious

adjective
in·​sid·​i·​ous | \ in-ˈsid-ē-əs How to pronounce insidious (audio) \

Medical Definition of insidious

: developing so gradually as to be well established before becoming apparent an insidious disease

Other Words from insidious

insidiously adverb

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Comments on insidious

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