adjective
Uncommon
insidious
ihn-SIH-dee-uhs
Insidious (adjective) means causing harm slowly and quietly, so the danger isn't obvious until real damage is done. Example: “The disease is insidious, showing almost no symptoms until it has spread.”
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."
Easily confused with
Common pairings
insidious disease
insidious effects
insidious threat
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Word forms
- Comparative
- more insidious
- Superlative
- most insidious
Fill the gap
Can you complete this real example?
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").
Synonyms
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Related words
Rhymes for insidious
See all rhymes for insidious →Frequently asked questions
What does “insidious” mean?
The word “insidious” means causing harm slowly and quietly, so the danger isn't obvious until real damage is done. In plain terms, something harmful that creeps up on you gradually rather than announcing itself.
How do you pronounce “insidious”?
“Insidious” is pronounced ihn-SIH-dee-uhs (/ɪnˈsɪdi.əs/ in IPA).
How do you use “insidious” in a sentence?
Here is “insidious” used in a sentence: “The disease is insidious, showing almost no symptoms until it has spread.”
What part of speech is “insidious”?
“Insidious” is an adjective.
Where does the word “insidious” come from?
The word “insidious” comes from Latin. From Latin insidiosus ("cunning, deceitful"), related to insidiae ("an ambush"), from insidere ("to sit in wait").
Is “insidious” a common word?
“Insidious” is an uncommon word in modern English.
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