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insidious Syllabification: in·sid·i·ous
Pronunciation: /inˈsidēəs/

Definition of insidious in English:


1Proceeding in a gradual, subtle way, but with harmful effects: sexually transmitted diseases can be insidious and sometimes without symptoms
More example sentences
  • Nuclear disc lesions are of gradual or insidious onset, the history may be on and off back pain for weeks and back pain getting worse.
  • The obstruction and harassment is subtle but insidious and seriously affects the ability of the aid agencies to do their job.
  • It need by no means be obvious: it can be insidious and subtle.
stealthy, subtle, surreptitious, cunning, crafty, treacherous, artful, sly, wily, shifty, underhanded, indirect
informal sneaky
1.1Treacherous; crafty: tangible proof of an insidious alliance
More example sentences
  • What they do is insidious, evil, and downright mean to their addict-victims like my wife.
  • They are, in my view, the most insidious of traitors.
  • Personally, we can't stand this insidious practise of sneaking adverts into non-commercial formats.


Mid 16th century: from Latin insidiosus 'cunning', from insidiae 'an ambush or trick', from insidere 'lie in wait for', from in- 'on' + sedere 'sit'.



Pronunciation: /inˈsidēəslē/
Example sentences
  • With an insidiously catchy melody the song dispensed every odious anti-Vietnam War cliche urged by the hippie/yippie crowd of 1967.
  • Sure, there might have been a few slightly over-the-top headlines, but that's only because Corby's defence team kept insidiously arguing that she was innocent.
  • The problem with the first approach is that the results are often trivial and insidiously biased; with the second, that you end up with a 250-page interview.


Pronunciation: /inˈsidēəsnəs/
Example sentences
  • But for five Irish teenagers, the magnifying glass doesn't reveal the insidiousness of California - it only inflates its lure and significance.
  • Slowly, with an insidiousness no one recognized, those businesses began to disappear until now many of the buildings sit empty and abandoned.
  • Asthma has become a common ailment in modern society, as the deteriorating environment and stress work their insidiousness against the human body.

Words that rhyme with insidious

fastidious, hideous, invidious, perfidious

Definition of insidious in:

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Pronunciation: ˈdo͞ofəs
a stupid person