insidious

adjective

in·sid·i·ous | \ in-ˈsi-dē-əs

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

Other Words from insidious insidious, sinister, or pernicious? More Example Sentences Learn More about insidious

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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.

Recent Examples on the Web

But there also is the possibility that long-term [e-cigarette] use may cause more insidious or chronic diseases from which there may not be a full recovery. — Kaiser Health News, oregonlive.com, "An early mysterious case of acute lung disease pointed to vaping," 24 Aug. 2019 But there also is the possibility that long-term [e-cigarette] use may cause more insidious or chronic diseases from which there may not be a full recovery. — Victoria Knight, Los Angeles Times, "Q&A: Vaping and lung disease: This doctor saw the link four years ago," 23 Aug. 2019 Now the town is known for something much more insidious. — Ann Killion, SFChronicle.com, "Former 49ers QB Jeff Garcia, a Gilroy native: ‘Our community will rise above’," 3 Aug. 2019 These innocent, innocuous, not-at-all-strange things become crucial plot points as the dark force known as the Mind Flayer returns in an insidious new form. — Tom Gliatto, PEOPLE.com, "Stranger Things 3 Is Even Better Than Season 2: Read PEOPLE's Review of Netflix's Fun-Creepy Hit," 1 July 2019 This sick longing for security is a dangerous thing, Meg, as insidious as the radiation from a nuclear explosion. — Meghan Cox Gurdon, WSJ, "Children’s Books: Stirring Up Fresh Life Endlessly," 21 Dec. 2018 Industry gurus talk about the insidious biological effects of emotional stress while shilling for stress-inducing lifestyles of strict diet, exercise, and meditation routines. — Brennan Kilbane, GQ, "The Least Stressful Way to Get Rid of Stress," 16 May 2018 The impact this will have on the bedrock principles of democratic U.S. governance is much more insidious. — Adam Weinstein, The New Republic, "Who Is Actually Running the U.S. Military’s Iran Efforts?," 18 June 2019 The last, and perhaps most insidious, factor: the advent of social media and its effect on weddings. — Sangeeta Singh-kurtz, Quartz, "Young Americans are racking up debt for Instagrammable weddings," 20 June 2019

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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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

See the full definition for insidious in the English Language Learners Dictionary

insidious

adjective

in·sid·i·ous | \ in-ˈsid-ē-əs

Medical Definition of insidious

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

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insidious

Definition of insidious

Other Words from insidious

insidious, sinister, or pernicious?

Examples of insidious in a Sentence

First Known Use of insidious

History and Etymology for insidious

English Language Learners Definition of insidious

Medical Definition of insidious

insidious

Definition of insidious

Other Words from insidious

insidious, sinister, or pernicious?

Examples of insidious in a Sentence

First Known Use of insidious

History and Etymology for insidious

English Language Learners Definition of insidious

Medical Definition of insidious

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