(1) 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"
(2) A persistently annoying person
(3) Any epidemic disease with a high death rate
(4) 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