insidious
adjective
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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
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.
Bruce Beehler, Baltimore Sun, 17 Aug. 2025
Even more insidious is the ability of some perennial weeds to reproduce from little vegetative bits that break off, roll down the hill, and make new problems.
—Paul Cappiello, The Courier-Journal, 15 Aug. 2025
The assassination of a beloved Palestinian-American activist in Southern California ignites a 40-year quest for justice, revealing the insidious roots of a dangerous political movement that thrives today.
—Katie Campione, Deadline, 2 Aug. 2025
At worst, these identical results amount to an insidious reproduction of the tropes and stereotypes present in the source text, as has been well documented by OpenAI’s own researchers.
—Piers Gelly
july 28, Literary Hub, 28 July 2025
See All Example Sentences for insidious
Cite this Entry
“Insidious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/insidious. Accessed 22 Aug. 2025.
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insidious
adjective
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insidious
adjective
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