Canker n. : 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.

Canker n. : Anything which corrodes, corrupts, or destroy.

Canker n. : A disease incident to trees, causing the bark to rot and fall off.

Canker n. : An obstinate and often incurable disease of a horse's foot, characterized by separation of the horny portion and the development of fungoid growths; -- usually resulting from neglected thrush.

Canker n. : A kind of wild, worthless rose; the dog-rose.

Canker v. t. : To affect as a canker; to eat away; to corrode; to consume.

Canker v. t. : To infect or pollute; to corrupt.

Canker v. i. : To waste away, grow rusty, or be oxidized, as a mineral.

Canker v. i. : To be or become diseased, or as if diseased, with canker; to grow corrupt; to become venomous.

Example:
What is a Canker sore and how do you alleviate the pain?

Taxonomy
canker, fungus Nectria, plant disease, free encyclopedia, plants, bacterium, lethal disease, organisms, Ash tree, bacterial canker, Dogwood anthracnose, stem canker, search, the human condition, Butternut trees, cure, birch, Beech tree.

Defination from the web:
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the ... The majority of canker-causing organisms are tied obligately to a single host species or genus, but a few will attack a wider range of plants. ...