01 a. Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons; as, the insidious foe.
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1.
Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons; as, the insidious foe.
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2.
Intended to entrap; characterized by treachery and deceit; as, insidious arts.“The insidious whisper of the bad angel.” — Hawthorne.
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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.
Phrases & compounds
Insidious disease —
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.
Syn.
Crafty; wily; artful; sly; designing; guileful; circumventive; treacherous; deceitful; deceptive.