can·ker 
(kăngkər)
(kăngkər)n.
1. Ulceration of the mouth and lips.
2. An inflammation or infection of the ear and auditory canal, especially in dogs and cats.
3. A condition in horses similar to but more advanced than thrush.
4.
a. A localized diseased or necrotic area on a plant part, especially on a trunk, branch, or twig of a woody plant, usually caused by fungi or bacteria.
b. Any of several diseases of plants characterized by the presence of such lesions.
5. A source of spreading corruption or decay.
v. can·kered, can·ker·ing, can·kers
v.tr.
1. To attack or infect with canker.
2. To infect with corruption or decay.
v.intr.
To become infected with or as if with canker.
[Middle English, from Old English cancer and from Old French cancre, both from Latin cancer, crab, malignant disease; see kar- in the Appendix of Indo-European roots.]
cankercanker on a rose stem