1. A corroding or sloughing ulcer; esp. a spreading gangrenous ulcer or collection of ulcers in or about the mouth; -- called also water canker, canker of the mouth, and noma. 2. Anything which corrodes, corrupts, or destroy. The cankers of envy and faction. Temple. 3. (Hort.) A disease incident to trees, causing the bark to rot and fall off. 4. (Far.) An obstina...