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.]
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,
The insidious whisper of the bad angel.Hawthorne.
3. Acting or proceeding unobserved or in a seemingly harmless manner, but slowly or eventually doing great damage; as, an
insidious disease; an
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.
adv. -- In*sid"i*ous*ness,
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Tue 18th December 2018