insidious

adjective in·sid·i·ous \ in-ˈsi-dē-əs \

|Updated on: 11 Jun 2018

Examples: insidious in a Sentence

Editor's Note: insidious, sinister, or pernicious?

Definition of insidious

1 a : awaiting a chance to entrap : treacherous

b : harmful but enticing : seductive

insidious drugs

2 a : 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

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insidiously

adverb

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insidiousness

noun

See insidious defined for English-language learners

See insidious defined for kids

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 of insidious from the Web

Despite the supposedly low expectations for this year, insidious optimism is gradually creeping back into England fans' minds as Russia approaches.

— SI.com, "2018 FIFA World Cup Team Preview: Analysing England's Chances at the Tournament," 5 June 2018
Now the woman who plays her, Lili Reinhart, is fighting back against another insidious enemy: Body-shaming rumors.

— refinery29.com, "Lili Reinhart Responds To Pregnancy Rumors, Though She Shouldn't Have To," 29 May 2018
That kind of insidious sweeping under the rug is exactly what enabled the behavior that, if not Tambor, some men have been exhibiting for decades.

— bridget read, Vogue, "After Jeffrey Tambor’s Behavior and the Excuses of His Male Castmates, Should You Watch the New Season of Arrested Development?," 25 May 2018
But this can also be seen in more subtle and insidious form in the way in which Brexit, for example, was campaigned for in terms of gut feelings and emotions rather than expert statistics and predictions.

— harry t dyer / the conversation, Ars Technica, "I watched an entire Flat Earth Convention for my research—here’s what I learned," 6 May 2018
Don't be racist These days, straight-up racists aside, more insidious forms of discrimination can and do creep in.

— nick levine, GQ, "Don't Be a Complete Jerk on Gay Dating Apps," 27 Apr. 2018
These initiatives aim to counter what may be the Trump administration's most insidious attacks on the Affordable Care Act: a proposal to expand the availability of short-term health plans.

— michael hiltzik, latimes.com, "States start pushing back against Trump's junky short-term health plans," 23 May 2018
But cancer cells’ ability to hide out in the body after an initial round of treatment is especially insidious.

— delia o'hara, Discover Magazine, "A Blood Test to Root Out Cancer," 18 May 2018
The Process is more insidious than Russian meddling.

— norman chad, San Antonio Express-News, "Norman Chad: Not trusting “The Process”," 9 Apr. 2018

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.

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.”