Definitions

from The American Heritage® Dictionary of the English Language, 4th 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Producing harm in a stealthy, often gradual, manner.
  • adj. Intending to entrap; alluring but harmful.
  • adj. Treacherous.

from the GNU version of the Collaborative International Dictionary of English

  • 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.

from The Century Dictionary and Cyclopedia

  • Lying in wait; hence, deceitful; sly; treacherous.
  • Designed or adapted to entrap; deceptive; insnaring: as, insidious arts.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adj. beguiling but harmful
  • adj. intended to entrap
  • adj. working or spreading in a hidden and usually injurious way

Etymologies

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)
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)

Examples

Comments

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  • Our research has shown that multitasking can have an insidious effect on learning.

    June 9, 2010

  • Men are so insidious!! Women, can I get an Amen!!

    March 14, 2010