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 But alongside all of these other more insidious factors affecting people’s uptake of the vaccine lies one less remarked about and far more simple: a fear of needles. Liam Hess, Vogue, 28 Apr. 2021 To read Frank together with Hopkin is to appreciate that technocratic, elite neoliberalism is as antidemocratic as explicit right-wing authoritarianism—and more insidious. Robert Kuttner, The New York Review of Books, 13 Apr. 2021 Da 5 Bloods, Ma Rainey’s Black Bottom, and Judas and the Black Messiah–were snubbed, and the only unifying factor is their Black casts and production teams, then something insidious is afoot. Zoe Guy, Marie Claire, 28 Feb. 2021 To tech’s critics, these definitional regularities point to something insidious, encapsulating in a word the dominance that each firm wields over its digital fief—some of it possibly ill-gotten. The Economist, 27 Feb. 2021 Covid-19 has presented us — children and adults alike — with a particularly insidious form of trauma for more than a year now. David Malebranche, STAT, 19 May 2021 Amid the ensuing shouts from the crowd were denunciations of a more insidious plague here in Kenya: public services that work for those with connections and money and relegate everyone else to the back of the line. Washington Post, 30 Mar. 2021 In the final insidious scenes, Minghella's character sets up the ultimate suspension trap for Samuel L. Jackson's crooked retired police chief Marcus Banks (Rock's onscreen father). Bryan Alexander, USA TODAY, 15 May 2021 If enacted, the law will help dismantle the insidious backyard breeding industry that makes buying a tiger cub easier than purchasing many breeds of domestic dogs. John Goodrich, CNN, 13 May 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

11 Jun 2021

Cite this Entry

“Insidious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/insidious. Accessed 14 Jun. 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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