insidious

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

|Updated on: 9 Jul 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

This fear is so pervasive, so insidious, that black people are being reprimanded for merely living.

— felice león, The Root, "Can We Live While Black?," 27 June 2018
By related logic, VR—duplicable and malleable—is a fraud, and an insidious one.

— spencer kornhaber, The Atlantic, "Westworld’s Virtual Afterlife Might Not Be Fiction," 27 June 2018
The behavioral design of these apps is sort of insidious in a really scary and nefarious way.

— clay skipper, GQ, "How to Be Happy When You're Skeptical of Everything," 3 May 2018
One possibility is that there’s an insidious side effect to all this innovation: People are hardly leaving their indoor habitats.

— stephanie walden, USA TODAY, "5 things the “Indoor Generation” can do to be happier and healthier," 15 May 2018
This is due to one insidious little insect known as the emerald ash borer (EAB).

— molly marquand, Good Housekeeping, "How To Attract Woodpeckers To Your Yard (And Why You'd Want To)," 13 June 2017
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

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.”