- 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
SynonymsSee more synonyms for on Thesaurus.com
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for insidiousness
We suspected not that deceit, insidiousness, and slavery were to be found beneath the sun.Imogen
Its insidiousness makes it exceedingly difficult to recognize.Outlines of dairy bacteriology
H. L. Russell
As to his character: it is too bad to associate him with so much craft and insidiousness.Christmas Penny Readings
George Manville Fenn
They believed in the personality, activity and insidiousness of the Devil.Unfettered
Sutton E. Griggs
The insidiousness of its design has been equalled only by the shameless manner of its being carried into execution.The Life of John Marshall (Volume 2 of 4)
Albert J. Beveridge
- stealthy, subtle, cunning, or treacherous
- working in a subtle or apparently innocuous way, but nevertheless deadlyan insidious illness
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
Word Origin and History for insidiousness
Online Etymology Dictionary, © 2010 Douglas Harper
- Being a disease that progresses with few or no symptoms to indicate its gravity.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.