Definition of Pest

Noun: pest pest

Any unwanted and destructive insect or other animal that attacks food or crops or livestock etc.
"he sprayed the garden to get rid of pests"; "many pests have developed resistance to the common pesticides"
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
- plague, pestilence, pestis
Any epidemic disease with a high death rate
- plague, pestilence
A persistently annoying person
- blighter, cuss, pesterer, gadfly