From WordNet (r) 3.0 (2006):
pest
n 1: 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 [syn:
plague, pestilence, pest, pestis]
2: any epidemic disease with a high death rate [syn: plague,
pestilence, pest]
3: a persistently annoying person [syn: pest, blighter,
cuss, pesterer, gadfly]
4: 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"