The meaning of INSIDIOUS is causing harm in a way that is gradual or not easily noticed; especially : having a gradual and cumulative negative effect. How to use insidious in a …

INSIDIOUS definition: 1. (of something unpleasant or dangerous) gradually and secretly causing harm: 2. (of something…. Learn more.

Usage What does insidious mean? Insidious describes something as being sneaky or being secretly dangerous or harmful.

If something is slowly and secretly causing harm, it's insidious — like the rumors no one seems to listen to until suddenly someone's reputation is ruined. Insidious is related to the Latin noun, …

Something that is insidious is unpleasant or dangerous and develops gradually without being noticed. The changes are insidious, and will not produce a noticeable effect for 15 to 20 years. …

1. Working or spreading harmfully in a subtle or stealthy manner: insidious rumors; an insidious disease. 2. Intended to entrap; treacherous: insidious misinformation. 3. Beguiling but harmful; …

spreading gradually or without being noticed, but causing serious harm. Definition of insidious adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example …

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.

dangerous through cunning, subtlety, and underhandedness. Their insidious plot included not only the assassination of President Lincoln but the killing of the Vice President and Secretary of …

Dec 14, 2025 · Intending to entrap; alluring but harmful. quotations Hansel and Gretel were lured by the witch’s insidious gingerbread house.