working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison" beguiling but harmful; "insidious pleasures
{s} crafty, cunning, deceitful; subtly treacherous or dangerous; deadly while appearing to be harmless
Insidious (în-sîd´ê-es) adjective 1 Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons 2 Intended to entrap; characterized by treachery and deceit Also: Insidious disease (Medical), a disease existing, without marked symptoms, but ready to become active upon some slight occasion; a disease not appearing to be as bad as it really is
working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison"
Something that is insidious is unpleasant or dangerous and develops gradually without being noticed. The changes are insidious, and will not produce a noticeable effect for 15 to 20 years + insidiously in·sidi·ous·ly Delusions are sometimes insidiously destructive. an insidious change or problem spreads gradually without being noticed, and causes serious harm (insidiosus, from insidiae , from insidere , from sedere )