Insidious Definition

Characterized by treachery or slyness; crafty; wily.
Webster's New World
Working harm in a slow or subtle manner; hence, more dangerous than seems evident.
An insidious disease.
Webster's New World
Intended to entrap; treacherous.
Insidious misinformation.
American Heritage
Beguiling but harmful; alluring.
Insidious pleasures.
American Heritage

Origin of Insidious

  • From Middle French insidieux, 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”).

    From Wiktionary

  • From Latin īnsidiōsus from īnsidiae ambush from īnsidēre to sit upon, lie in wait for in- in, on in–2 sedēre to sit sed- in Indo-European roots

    From American Heritage Dictionary of the English Language, 5th Edition

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