Insidiously

2 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Insidious \In*sid"i*ous\, a. [L. insidiosus, fr. insidiae an
     ambush, fr. insidere to sit in; pref. in- + sedere to sit:
     cf. F. insidieux. See {Sit}.]
     [1913 Webster]
     1. Lying in wait; watching an opportunity to insnare or
        entrap; deceitful; sly; treacherous; -- said of persons;


        as, the insidious foe. "The insidious witch." --Cowper.
        [1913 Webster]
  
     2. Intended to entrap; characterized by treachery and deceit;
        as, insidious arts.
        [1913 Webster]
  
              The insidious whisper of the bad angel. --Hawthorne.
        [1913 Webster]
  
     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.
        [PJC]
  
     {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.
          [1913 Webster]

From WordNet (r) 2.0 [wn]:

  insidiously
       adv : in a harmfully insidious manner; "these drugs act
             insidiously" [syn: {perniciously}]