1. (noun)canker a fungal disease of woody plants that causes localized damage to the bark
2. (noun)canker, canker sore an ulceration (especially of the lips or lining of the mouth)
3. (noun)pestilence, canker 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"