pest

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An annoying person or thing; a nuisance.
• noun An organism, typically an insect, that sickens or annoys humans, hampers human activities, damages crops or food products, harms livestock, or causes damage to buildings.
• noun A deadly epidemic disease; a pestilence.

from The Century Dictionary.

• noun Plague; pestilence; a deadly epidemic disease.
• noun Any very noxious, mischievous, or destructive thing, or a mischievous, destructive, very annoying, or troublesome person.
• noun Synonyms Infection.
• noun Scourge, nuisance.

from the GNU version of the Collaborative International Dictionary of English.

• noun A fatal epidemic disease; a pestilence; specif., the plague.
• noun Anything which resembles a pest; one who, or that which, is troublesome, noxious, mischievous, or destructive; a nuisance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun originally A plague, pestilence, epidemic
• noun An annoying, harmful, often destructive creature.
• noun An annoying person.
• noun UK, slang Someone with poor social discipline who continually bothers disinterested women.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a serious (sometimes fatal) infection of rodents caused by Yersinia pestis and accidentally transmitted to humans by the bite of a flea that has bitten an infected animal
• noun a persistently annoying person
• noun any epidemic disease with a high death rate
• noun any unwanted and destructive insect or other animal that attacks food or crops or livestock etc.