Any epidemic disease that is highly contagious, infectious, virulent and devastating. / (archaic) Anything harmful to morals or public order.

plural of pestilence

The personification of pestilence, often depicted riding a white horse.

Highly injurious or destructive to life: deadly. / (informal) Annoying. / (archaic) Harmful to morals or public order.

In a pestilent manner.

(obsolete) The act of pounding and bruising with a pestle in a mortar.