adjective in·sid·i·ous \in-ˈsi-dē-əs\

: causing harm in a way that is gradual or not easily noticed

Full Definition of INSIDIOUS

a :  awaiting a chance to entrap :  treacherous
b :  harmful but enticing :  seductive <insidious drugs>
a :  having a gradual and cumulative effect :  subtle <the insidious pressures of modern life>
b of a disease :  developing so gradually as to be well established before becoming apparent
in·sid·i·ous·ly adverb
in·sid·i·ous·ness noun

Examples of INSIDIOUS

  1. Most people with this insidious disease have no idea that they are infected.
  2. But the litigation is also prompting a subtle and insidious change in the way that medicine is practiced, which affects anyone who consults a health professional, even if they would not dream of setting foot in a lawyer's office. It is known as defensive medicine. —Geoff Watts, New Scientist, 23–29 Oct. 2004


Latin insidiosus, from insidiae ambush, from insidēre to sit in, sit on, from in- + sedēre to sit — more at sit
First Known Use: 1545

Rhymes with INSIDIOUS

Medical Dictionary


adjective in·sid·i·ous \in-ˈsid-ē-əs\

Medical Definition of INSIDIOUS

:  developing so gradually as to be well established before becoming apparent <an insidious disease>
in·sid·i·ous·ly adverb


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