insidious

[ in-sid-ee-uhs ]

See synonyms for: insidious insidiously insidiousness on Thesaurus.com

adjective

intended to entrap or beguile: an insidious plan.
stealthily treacherous or deceitful: an insidious enemy.

operating or proceeding in an inconspicuous or seemingly harmless way but actually with grave effect: an insidious disease.

Origin of insidious

First recorded in 1535–45; from Latin insidiōsus “deceitful,” from insidi(ae) (plural) “an ambush” (from insidēre “to sit in”) + -ōsus -ous;see also sit¹

Other words for insidious

1	corrupting
2	artful, cunning, wily, subtle, crafty

See synonyms for insidious on Thesaurus.com

Other words from insidious

in·sid·i·ous·ly, adverb
in·sid·i·ous·ness, noun
un·in·sid·i·ous, adjective
un·in·sid·i·ous·ly, adverb
un·in·sid·i·ous·ness, noun

Words that may be confused with insidious

insidious , invidious

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use insidious in a sentence

Overlapping constellations of reasons drove this—such areas house more essential workers, living in more crowded homes, with less access to health care—but among the more insidious was chronic exposure to air pollution.
At New York City’s biggest power plant, a switch to clean energy will help a neighborhood breathe easier | Andrew Blum | February 2, 2021 | Popular-Science
Maybe this car-seat situation is a perfect illustration of the insidious way we sometimes settle for solutions that satisfy everyone except the constituency those solutions were intended to help.
How Much Do We Really Care About Children? (Ep. 447) | Stephen J. Dubner | January 14, 2021 | Freakonomics
For everything AI can do, it’s flawed at defending insidious attacks targeting its input data.
2021 Could Be a Banner Year for AI—If We Solve These 4 Problems | Shelly Fan | January 5, 2021 | Singularity Hub
Nonetheless, misleading stories that percolate less widely can still have an insidious influence.
Vaccine hoaxes are rampant on social media. Here’s how to spot them. | Rachel Lerman | December 18, 2020 | Washington Post
Taking into account some models’ ability to filter out more harmful and more insidious particles like viruses and VOCs, an air purifier can be one of the easiest and most subtle ways to improve your daily quality of life.
Best air purifier: Fight allergens, smoke, and germs for cleaner indoor air | PopSci Commerce Team | December 17, 2020 | Popular-Science

She saw O-liver start from his chair and sink back, helpless against the insidiousness of this attack.
The Gay Cockade | Temple Bailey
The constancy and the strength of temptation, and the insidiousness of the arguments it was supported by, has been proverbial.
Is Life Worth Living? | William Hurrell Mallock
Indeed, it is perhaps more damaging in its secondary effects because of its insidiousness.
Honest Money | Arthur Isaac Fonda
But this lent a new insidiousness to his temptation, since her contempt would be a refuge from his own.
The Touchstone | Edith Wharton
Its insidiousness makes it exceedingly difficult to recognize.
Outlines of dairy bacteriology | H. L. Russell

British Dictionary definitions for insidious

insidious

/ (ɪnˈsɪdɪəs) /

adjective

stealthy, subtle, cunning, or treacherous
working in a subtle or apparently innocuous way, but nevertheless deadly: an insidious illness

Origin of insidious

C16: from Latin insidiōsus cunning, from insidiae an ambush, from insidēre to sit in; see insessorial

Derived forms of insidious

insidiously, adverb
insidiousness, noun

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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