Insidious
Insidious , adjective
[Latin insidiosus, from insidiae an ambush, from insidere to sit in; pref. in- + sedere to sit: compare French insidieux. See Sit.]
1.
Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons; as, the insidious foe.
The insidious witch.
2.
Intended to entrap; characterized by treachery and deceit; as, insidious arts.
The insidious whisper of the bad angel.
3.
Acting or proceeding unobserved or in a seemingly harmless manner, but slowly or eventually doing great damage; as, an insidious disease; an insidious plot.
Collocations (1)
Insidious disease (Medicine) , 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.