insidious

/ɪnˈsɪdiəs/
adjective
  1. Proceeding in a gradual, subtle way but with harmful effects.
    • The insidious spread of mold in the walls went unnoticed for months.
    • She warned about the insidious influence of biased news on public opinion.
    • An insidious disease can show no symptoms until it is advanced.
  2. Intended to entrap or deceive; treacherous.
    • The spy used insidious tricks to gain access to the classified files.
    • The con artist's insidious plan slowly drained the victims' savings.
    • His insidious compliments were actually meant to undermine her confidence.
What does "insidious" mean? | whatsthatwordmean | whatsthatwordmean