Pest (noun)

1. An animal or insect that is harmful to plants or crops.
2. A person or thing that is annoying or causing trouble.
3. A contagious disease that spreads rapidly and causes many deaths.

Origin:

From the old english pest, from the latin pestis "plague, pestilence".

Examples:

1. The aphid is a common pest in gardens.
2. The pest kept bothering her with constant phone calls.
3. The pest spread rapidly through the city.
4. The pest ruined the crops.
5. The pest was finally eliminated.