# insidious

> English word · Adjective · IPA /ɪnˈsɪdi.əs/ · frequency rank #21,246

## Definitions
1. Causing harm in a stealthy, often gradual, manner.
2. Intending to entrap; alluring but harmful.
3. Treacherous.

## Etymology
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”).

## Common misspellings (12)
`inisdious`, `innsidious`, `insdiious`, `insiddious`, `insidiosu`, `insidiouss`, `insidiuos`, `insidoius`, `insiidous`, `inssidious`, `isnidious`, `nisidious`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/insidious