DICT.TW Dictionary Taiwan

 In·sid·i·ous a.
 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.   --Hawthorne.
 Insidious disease Med., 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.
 -- In*sid*i*ous*ly, adv. -- In*sid*i*ous*ness, n.
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 insidiousness
      n 1: subtle and cumulative harmfulness (especially of a disease)
      2: the quality of being designed to entrap