insidious

[ in-sid-ee-uhs ]

adjective

1. intended to entrap or beguile:

   an insidious plan.

2. stealthily treacherous or deceitful:

   an insidious enemy.

   Synonyms: crafty, subtle, wily, cunning, artful

3. operating or proceeding in an inconspicuous or seemingly harmless way but actually with grave effect:

   an insidious disease.

insidious

/ ɪnˈsɪdɪəs /

adjective

1. stealthy, subtle, cunning, or treacherous
2. working in a subtle or apparently innocuous way, but nevertheless deadly

   an insidious illness

Derived Forms

• inˈsidiousness, noun
• inˈsidiously, adverb

Other Words From

• in·sidi·ous·ly adverb
• in·sidi·ous·ness noun
• unin·sidi·ous adjective
• unin·sidi·ous·ly adverb
• unin·sidi·ous·ness noun

Word History and Origins

Origin of insidious¹

First recorded in 1535–45; from Latin insidiōsus “deceitful,” from insidi(ae) (plural) “an ambush” (from insidēre “to sit in”) + -ōsus -ous; sit ¹

Word History and Origins

Origin of insidious¹

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

Example Sentences

Is it anti-Semitism, or are less insidious cultural forces at work?

From The Daily Beast

But its far more insidious role was revealed, whether it was gun policies or voter suppression.

From The Daily Beast

The act of erasure through mis- or under-representation is an insidious one.

From The Daily Beast

Its insidious reach enters into medical offices and chokes off the free-speech rights of the people trying to work there.

From The Daily Beast

But the commentary that McCarthy gets from her so-called supporters is often just as cruel, but somehow more insidious.

From The Daily Beast

Play-writing is a luxury to a journalist, as insidious as golf and much more expensive in time and money.

From Project Gutenberg

Each cachet contained three decigrams of malourea, the insidious drug notorious under its trade name of Veronal.

From Project Gutenberg

The state of affairs which has come about was uncertain in origin, insidious in growth, and has developed over a wide field.

From Project Gutenberg

She believed he sought her, and she must needs fight an insidious liking for him.

From Project Gutenberg

This is a thing I would despise in anybody else; but he is so jolly insidious 240 and ingratiating!

From Project Gutenberg

Related Words

• dangerous
• subtle