Definition of "Pest" :

noun: 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."

noun: a persistently annoying person

noun: any epidemic disease with a high death rate

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