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insidious

in·sid·i·ous

insidious

 
 
pronunciation:
ihn sI di s
part of speech: adjective
definition 1: dangerous through cunning, subtlety, and underhandedness.
Their insidious plot included not only the assassination of President Lincoln but the killing of the Vice President and Secretary of State as well.
definition 2: seemingly or outwardly harmless, but actually very dangerous.
Glaucoma is an insidious disease that can damage a person's eyes before causing any symptoms.an insidious philosophy
derivations: insidiously (adv.), insidiousness (n.)