Bubonic plague: An infectious disease that is caused by the bacterium Yersinia pestis and is transmitted to humans from infected rats by the oriental rat flea. It is named for the characteristic feature of buboes (painfully enlarged lymph nodes) in the groin, armpits, neck, and elsewhere. Other symptoms of bubonic plague include headache, fever, chills, and weakness. Bubonic plague can lead to gangrene (tissue death) of the fingers, toes, and nose. Also called Black Death and Black Plague.