Other forms: pests
A pest is something or someone that bugs you. That annoying mosquito that keeps you up at night is a pest, and so is that younger brother who wants to control the TV remote.
An unwanted, bothersome person is a pest — and so is an unwanted, bothersome bug. In fact, the "destructive or harmful insect" definition came before "annoying person," following the "plague or pestilence" meaning of pest. The Latin root is pestis, "deadly contagious disease." During the Late Middle Ages, when the bubonic plague killed a third of all humans, it was commonly known as "the pest."