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Meaning of insidious

in•sid•i•ous

Pronunciation: (in-sid'ē-us), [key]
— adj.
  1. intended to entrap or beguile: an insidious plan.
  2. stealthily treacherous or deceitful: an insidious enemy.
  3. operating or proceeding in an inconspicuous or seemingly harmless way but actually with grave effect: an insidious disease.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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