adjective
insidious
ihn-SIH-dee-uhs
adjective
1
Causing harm slowly and quietly, so the danger isn't obvious until real damage is done.
"The disease is insidious, showing almost no symptoms until it has spread."
"Prejudice can be insidious, shaping opinions before people notice it happening."
How to Use Insidious
Learner’s notesIn plain EnglishSomething harmful that creeps up on you gradually rather than announcing itself.
Common mistake
Insidious describes gradual, hidden harm — it isn't simply a fancier word for "bad" or "evil."
Common pairings
insidious disease
insidious effects
insidious threat
Word Forms
more insidious comparative, most insidious superlative
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The disease is _____, showing almost no symptoms until it has spread.
Etymology
From Latin insidiosus ("cunning, deceitful"), related to insidiae ("an ambush"), from insidere ("to sit in wait").