pernicious

Pernicious describes harm that spreads slowly and gets worse over time, often hidden inside something that looks harmless. It comes from Latin pernicies, destruction. A pernicious habit, a pernicious rumour: each does a little more damage every day. It is close to insidious, but pernicious stresses how much harm is finally done. In the animation, a smiling man lets a small bug rest on his finger while it eats his coat to rags.