insidious

adjective

in·sid·i·ous in-ˈsi-dē-əs

Synonyms of insidious next

: having a gradual and cumulative effect : subtle

the insidious pressures of modern life

of a disease : developing so gradually as to be well established before becoming apparent

: awaiting a chance to entrap : treacherous

: harmful but enticing : seductive

insidious drugs

insidiously adverb

insidiousness noun

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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 There are also more insidious ways climate change takes a bite out of the US economy. —

Justine Calma, The Verge, 14 Nov. 2023 But videos like this may be responsible for a more insidious type of erosion: undermining trust in media at large. —

IEEE Spectrum, 9 Nov. 2023 The discrimination Black women face is particularly insidious, and manifests in racial stereotypes and microaggressions. —

Kushie Amin, refinery29.com, 30 Oct. 2023 Read More: Indigenous Lands Could Help Threatened Primate Populations The Deforestation of Spider Monkeys in the Rainforest Deforestation, which drives habitat loss and fragmentation, is a more insidious threat to spider monkeys. —

Anna Nordseth, Discover Magazine, 15 Aug. 2023 But this stuff could have an insidious hand in that. —

Ethan Shanfeld, Variety, 5 Oct. 2023 Many people don’t understand how insidious verbal abuse is or how an abusive partner can hold such sway over intelligent and capable adults. —

Meghan Leahy, Washington Post, 4 Oct. 2023 Scorsese intently observes the arachnid manner with which King turns Ernest from outsider to insider, which is accomplished in the insidious span of a single welcoming conversation. —

Richard Brody, The New Yorker, 20 Oct. 2023 Six years after Unite the Right, an insidious new brand of antisemitism has taken hold in Charlottesville, home to the University of Virginia. —

Anna Kriebel, National Review, 17 Oct. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'insidious.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.