insidious.
Causing harm in a stealthy, often gradual, manner.
Meaning & usage
Causing harm in a stealthy, often gradual, manner.
Intending to entrap; alluring but harmful.
Hansel and Gretel were lured by the witch’s insidious gingerbread house.
Treacherous.
The battle was lost due to the actions of insidious defectors.
Where this word comes from
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”).
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Definitions, grammatical labels, IPA, etymology and examples: Wiktionary contributors, extracted by Kaikki / Wiktextract. Adapted under CC BY-SA 4.0. Selected fields and authored examples are shown; third-party quotations and audio are omitted. See contributor history.
Last enriched 2026-09-10. Definitions are in English. Romanizations are shown when supplied by the source; syllable estimates are omitted for unsupported scripts.