canker

(noun) a fungal disease of woody plants that causes localized damage to the bark.

(noun) an ulceration (especially of the lips or lining of the mouth). Synonyms: canker sore.

(noun) a pernicious and malign influence that is hard to get rid of. Synonyms: pestilence. Examples: "Racism is a pestilence at the heart of the nation." "According to him, i was the canker in their midst."

(verb) become infected with a canker.

(verb) infect with a canker.