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 sentence. insidious, …

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

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

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; alluring: …

Definition of insidious adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

insidious (adjective) insidious /ɪn ˈ sɪdijəs/ adjective Britannica Dictionary definition of INSIDIOUS [more insidious; most insidious] formal : causing harm in a way that is gradual or not easily noticed

Insidious definition: Working or spreading harmfully in a subtle or stealthy manner.

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, īnsidiae …

Nov 27, 2025 · insidious (comparative more insidious, superlative most insidious) Causing harm in a stealthy, often gradual, manner. synonym quotations Synonym: subtle

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. They focus on …