Insidious Definition

ĭn-sĭdē-əs

adjective

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

The definition of insidious is something or someone who works in a subtle or sly way, or in an intent to trap.

An example of insidious is a plan that is meant to scam people out of money.

YourDictionary

Synonyms:

Antonyms:

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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