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

“We understood the Soviet Union was an existential threat, certainly with its nuclear capabilities, it was, and Russia is, but China is even more sinister. It's more insidious in what they have done under this communist regime.”

From Salon

On the right came a wealthy real estate baron who blamed immigrants, the "deep state" and other insidious actors for America's decline.

From Salon

On the right came a real estate baron who blamed immigrants, the "deep state" and other insidious actors.

From Salon

He told BBC Scotland News: "There was no smoking gun - the delay isn't down to some insidious conspiracy to frustrate the road, but there was a complete lack of transparency and clarity about the funding of this road."

From BBC

And while many insidious and long-reaching national traumas eventually manifest as horror movies like The Exorcist and Get Out, many others curdle into horror of a darker kind because, after all, every person’s dream of a perfect society is someone else’s nightmare.

From Slate

Related Words

• dangerous
• subtle