insidious

[ in-sid-ee-uhs ]

/ ɪnˈsɪd i əs /

SEE MORE SYNONYMS FOR insidious 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.

Nearby words

inside track, inside track, the, insider, insider dealing, insider trading, insidious, insight, insightful, insigne, insignia, insignificance

Origin of insidious

1535–45; < Latin insidiōsus deceitful, equivalent to insidi(ae) (plural) an ambush (derivative of insidēre to sit in or on) + -ōsus -ous; see sit¹

SYNONYMS FOR insidious

1 corrupting.

2 artful, cunning, wily, subtle, crafty.

SEE MORE SYNONYMS FOR insidious ON THESAURUS.COM

Related forms

in·sid·i·ous·ly, adverbin·sid·i·ous·ness, nounun·in·sid·i·ous, adjectiveun·in·sid·i·ous·ly, adverb

un·in·sid·i·ous·ness, noun

Can be confused

insidious invidious

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for insidious

The act of erasure through mis- or under-representation is an insidious one.
It Ain't Easy Being Bisexual on TV|Amy Zimmerman|August 14, 2014|DAILY BEAST
Its insidious reach enters into medical offices and chokes off the free-speech rights of the people trying to work there.
Pediatricians Have the Right to Ask About Guns|Russell Saunders|July 30, 2014|DAILY BEAST
Cancer is the most pernicious, insidious, disgusting disease of life.
Pierce Brosnan’s Life After Bond: From Action Hero to Losing His Daughter to Cancer|Tim Teeman|July 2, 2014|DAILY BEAST
However, an insidious form of segregation, happening within the educational system, belies this simplistic view.
Roma Children Face Segregation In EU Schools|Amana Fontanella-Khan|March 8, 2014|DAILY BEAST

This would be dismissible, but it actually had an insidious impact.
Bob Woodward and the Rules of Washington Morality|Michael Tomasky|March 3, 2013|DAILY BEAST
The insidious revolt led by Buck had destroyed the solidarity of the team.
The Call of the Wild|Jack London
That last deceptive stage of his insidious disease had given him a fictitious strength.
The Ebbing Of The Tide|Louis Becke
And we know what are the paths by which Athenian aggression travels, and how insidious is its progress.
The History of the Peloponnesian War|Thucydides
I never dreamed of jealousy, Alfred Bernard, or I might have seen beforehand the wiles of the insidious tempter.
Hansford: A Tale of Bacon's Rebellion|St. George Tucker
At the next meeting of parliament, the king agreed to omit these insidious words, p. 168.
View of the State of Europe during the Middle Ages, Vol. 3 (of 3)|Henry Hallam

British Dictionary definitions for insidious

insidious

/ (ɪnˈsɪdɪəs) /

adjective

stealthy, subtle, cunning, or treacherous

working in a subtle or apparently innocuous way, but nevertheless deadlyan insidious illness

Derived Forms

insidiously, adverbinsidiousness, noun

Word Origin for insidious

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

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

Medicine definitions for insidious

insidious

[ ĭn-sĭd′ē-əs ]

adj.

Being a disease that progresses with few or no symptoms to indicate its gravity.

Related forms

in•sid′i•ous•ly adv.