insidious

Adjective
Synonyms: pernicioussubtle

WordNet 3.0

Adjective (3)

  1. beguiling but harmful“insidious pleasures”
  2. intended to entrap
  3. working or spreading in a hidden and usually injurious way“glaucoma is an insidious disease”“a subtle poison”Synonyms: pernicioussubtle
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Webster's Dictionary (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]

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