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Definitions

insidious

[in-sid-ee-uhs] / ɪnˈsɪd i əs /
ADJECTIVE
sneaky, tricky
Synonyms
STRONGEST
dangerous subtle
WEAK
Machiavellian artful astute corrupt crafty crooked cunning deceitful deceptive deep designing dishonest disingenuous duplicitous ensnaring false foxy guileful intriguing like a snake in the grass perfidious perilous secret slick sly smooth snaky sneaking stealthy surreptitious treacherous wily wormlike
Antonyms
WEAK
fair honest open sincere

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

It’s a subtle shift where “treat yourself” moments — like frequent dinners out or luxury upgrades — slowly morph into consistent, insidious monthly expenses.

From MarketWatch • Apr. 7, 2026

Times columnist Patt Morrison, Smoglandia traces the rise, impact, and retreat of the city’s most insidious pollution.

From Los Angeles Times • Mar. 26, 2026

"The cold is a very insidious enemy, it should not be underestimated," she said.

From Barron's • Feb. 16, 2026

Mines are some of the most insidious and long-lasting legacies of war.

From BBC • Jan. 30, 2026

And even through the children’s laughter there’s this insidious silence that underscores everything; then again, maybe the silence was always there, and I’m only just noticing it now.

From "Dry" by Neal Shusterman and Jarrod Shusterman