canker

Noun

• a pernicious and malign influence that is hard to get rid of
  • racism is a pestilence at the heart of the nation
    
  • according to him, I was the canker in their midst
    

• an ulceration (especially of the lips or lining of the mouth)

• a fungal disease of woody plants that causes localized damage to the bark

Verb

• infect with a canker

• become infected with a canker

Related words

• Synonyms: 
  pestilence , canker sore