Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- adj. Working or spreading harmfully in a subtle or stealthy manner: insidious rumors; an insidious disease.
- adj. Intended to entrap; treacherous: insidious misinformation.
- adj. Beguiling but harmful; alluring: insidious pleasures.
Century Dictionary and Cyclopedia
- Lying in wait; hence, deceitful; sly; treacherous.
- Designed or adapted to entrap; deceptive; insnaring: as, insidious arts.
Wiktionary
- adj. Producing harm in a stealthy, often gradual, manner.
- adj. Intending to entrap; alluring but harmful.
- adj. nonstandard Treacherous.
GNU Webster's 1913
- adj. Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons.
- adj. Intended to entrap; characterized by treachery and deceit.
- adj. Acting or proceeding unobserved or in a seemingly harmless manner, but slowly or eventually doing great damage.
WordNet 3.0
- adj. beguiling but harmful
- adj. intended to entrap
- adj. working or spreading in a hidden and usually injurious way
Etymologies
- From Latin īnsidiōsus ("cunning, artful, deceitful"), from īnsidiae ("a lying in wait, an ambush, artifice, stratagem") + -ōsus, from īnsideō ("to sit in or on"), from in ("in, on") + sedeō ("to sit"). (Wiktionary)
- From Latin īnsidiōsus, from īnsidiae, ambush, from īnsidēre, to sit upon, lie in wait for : in-, in, on; see in-2 + sedēre, to sit; see sed- in Indo-European roots. (American Heritage® Dictionary of the English Language, Fourth Edition)
Examples
“I mean, you've got Darth Sidious (as in "insidious," I assume) and then the even-more-obviously named Darths Maul and Tyrannus.”
“The greatest dangers to liberty lurk in insidious encroachment by men of zeal, well-meaning but without understanding.”
The Volokh Conspiracy » Ninth Circuit Denies Rehearing in Al-Kidd v. Ashcroft
“But I fear the most insidious is because people think that changing their lightbulbs and sorting their recyclables counts as “doing your bit”.”
“In my opinion, one of the more insidious is the hijacked account scam.”
“Far more insidious is Lieberman, with his coprophagic grin and his profession of good will.”
“What makes Huffington Post more insidious is the way they can buy of dissent readily by giving an organization their own blog.”
On Gaza: Huffington Post Takes Cues From Fox News « Antiwar.com Blog
“The greatest dangers to liberty lurk in insidious encroachment by men of zeal, well meaning but without understanding.”
“The latest strategy is now seen dropping unsupported accusations across the media spectrum to the effect that the intelligence agency's assignment of Ambassador Joseph Wilson to look into the now-discredited Iraq/Niger/uranium claims were all part of a long-term insidious scheme to try and discredit the Bush Administration.”
“Less obvious, but more insidious, is the prejudice against skin color: dark, not light, is the dominant complexion.”
“insidious movie violence" Los Angeles - One of the most violent movie stars of all time has come out against what he calls insidious movie violence.”
Lists
These user-created lists contain the word ‘insidious’.
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Test Prep or Just for fun
Building a list for standardized test prep or just for learning some new words! Please add any words that you feel are important for the SAT/GRE/GMAT etc...
throng, morass, parley, facile, kismet, strife, jetsam, carrion, annex, harbinger, vestige, surreptitious and 575 more...
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GRE Barrons Wordlist
A complete Barron's Wordlist for GRE preparation. Your online flashcard replacement.
abase, abash, abate, abbreviate, abdicate, aberrant, aberration, abet, abeyance, abhor, abject, abjure and 4087 more...
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7thGradeWords
horde, doggedly, retina, frail, jovial, insidious, injudicious, brazen, tentative, hortle, adaver, benign and 91 more...
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macabre
words associated with the macabre & horror.
( open list, randomness )
more:
http://www.wordnik.co...ghastly, grisly, culeus, silly, gruesome, horrid, morbid, angelic, shocking, hideous, ghoulish, frightful and 136 more...
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movement (slow)
words describing slow action or movement
( open list, randomness, descriptive )
related:
http://www.wordnik.co...creep, crawl, plod, slouch, idle, lumber, tiptoe, bend, amble, mosey, saunter, loiter and 117 more...
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GRE 2014
abate, abdicate, abase, aberrant, abeyance, abhor, abjure, abortive, abound, abrasive, abreast, abridge and 1577 more...
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EN-HU - important words for a HU inte...
Words only (I left out the expressions) from Geza Kerenyi's EN-HU interpreters' dictionary. Most of them pose some difficulty when interpreted between HU and EN in either or both directions.
abalone, abrasive, abstractionist, abstruse, abysmal, academia, accessibility, accessible, acclimate, accolade, accompanist, achiever and 1469 more...
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Burroughs
Detestable words
purulence, bête noire, exigent, exculpate, desideratum, lucriferous, concomitant, pertinacious, pervicacious, gemütlichkeit, sublimate, sanfroid and 38 more...
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rolls off the tongue
Words you love saying because they feel and sound so good!
(Not to be conflated with words you love saying because they are onomatopoeic, I have another list for that)gubernatorial, predeliction, quibbling, propensity, proclivity, insidious, nebulous, garble, crabapple, piddling, prattle, wheedling and 11 more...
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Misanthropic
Lovecraft, Lovecraftian, bete noire
Lovecraftian, bête noire, festinate, hathos, misogynist, foredoom, decorticate, malingerer, nemophilist, mendicant, pendragon, stultify and 27 more...
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Words that Julio has taught me
panegyric, encomium, navigable, gerrymander, carpetbagging, insidious, ribald, vilify, epithalamion, cogent, deprecate, apocryphal
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big book gre
abase, abbess, abbey, abbot, abdicate, abdomen, abdominal, abduction, abed, aberration, abet, abeyance and 6691 more...
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Harmful
quick, hurtful, ruinous, noxious, destructive, deadly, mischievous, deleterious, baneful, injurious, baleful, malicious and 24 more...
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gre2
aberrant, aberration, aboveboard, abrasive, abstemious, acme, admonish, affable, affluent, alacrity, allegory, alleviate and 1861 more...
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All The Words
I enjoy collecting words, for I have no fear of them ever running out.
tatterdemalion, panopticon, idioglossia, hypnagogue, hypnopomp, defenestration, anacoluthon, scofflaw, affront, edifying, palimpsest, naufrage and 475 more...
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Twitter favourites
The new favourite words of people on Twitter.
A script searches Twitter for "X is my new favourite word" and adds it to this list.
See also:
bumwank, calamity, recalcitrant, gayenese, jeeze, nonsense, flabbergasted, juxtapose, procrastinating, ossanity, biffing, loser and 1972 more...
Tweets
Looking for tweets for insidious.

jwjarvis Our research has shown that multitasking can have an insidious effect on learning. Jun 9, 2010
Michelle Scott-Wilson Men are so insidious!! Women, can I get an Amen!! Mar 13, 2010