/pest/ , n.
1. an annoying or troublesome person, animal, or thing; nuisance.
2. an insect or other small animal that harms or destroys garden plants, trees, etc.
3. a deadly epidemic disease, esp. a plague; pestilence.
[ 1545-55; pestis plague ]
Syn. 1. annoyance. 3. pandemic, scourge, epidemic.