in·sid·i·ous
adjective \in-ˈsi-dē-əs\
: causing harm in a way that is gradual or not easily noticed
Full Definition of INSIDIOUS
1a : awaiting a chance to entrap : treacherous
b : harmful but enticing : seductive <insidious drugs>
2a : 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
Origin of INSIDIOUS
Latin insidiosus, from insidiae ambush, from insidēre to sit in, sit on, from in- + sedēre to sit — more at sit
First Known Use: 1545
in·sid·i·ous
adjective \in-ˈsid-ē-əs\ (Medical Dictionary)
Medical Definition of INSIDIOUS
: developing so gradually as to be well established before becoming apparent <an insidious disease>
—in·sid·i·ous·ly adverb