canker

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Ulceration of the mouth and lips.
• noun An inflammation or infection of the ear and auditory canal, especially in dogs and cats.
• noun A condition in horses similar to but more advanced than thrush.
• noun 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.
• noun Any of several diseases of plants characterized by the presence of such lesions.
• noun A source of spreading corruption or decay.
• intransitive verb To attack or infect with canker.
• intransitive verb To infect with corruption or decay.
• intransitive verb To become infected with or as if with canker.

from The Century Dictionary.

• To infect with canker, either literally or figuratively; eat into, corrode, or corrupt; infect as with a poisonous influence; render ill-conditioned or venomous; make sour and ill-natured.
• To corrode; grow corrupt; be infected with some poisonous or pernicious influence; be or become ill-conditioned or malignant.
• To fret; become peevish.
• To decay or waste away by means of any noxious cause; grow rusty or discolored by oxidation, as a metal.
• noun A cancerous, gangrenous, or ulcerous sore or disease, whether in animals or plants; hence, any corroding or other noxious agency producing ulceration, gangrene, rot, decay, etc.
• noun Specifically— Cancrum oris (which see, under cancrum).
• noun A disease or fungus attacking trees or other plants and causing slow decay.
• noun In farriery, a disease in horses' feet, causing a discharge of fetid matter from the cleft in the middle of the frog, generally originating in a diseased thrush.
• noun A canker-worm or insect-larva that injures plants by feeding on them.
• noun Figuratively, anything that corrodes, corrupts, destroys, or irritates; irritation; pain; grief; care.
• noun Rust.
• noun In botany: The canker-rose or field-poppy, Papaver Rhæas.
• noun The wild dogrose, Rosa canina.
• noun A toadstool.
• noun An irregular excrescence on the trunks or branches of woody plants, caused by the perennial effort of the tissues to overcome an injury. Cankers may be originated by various causes, such as accidental wounds, injuries by frost, insects, fungi or bacteria, or various combinations of these.
• noun A disease of fowls affecting the mouth and windpipe. It produces ulceration and often ends in death.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun Anything which corrodes, corrupts, or destroy.
• noun (Hort.) A disease incident to trees, causing the bark to rot and fall off.
• noun (Far.) 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.
• noun A kind of wild, worthless rose; the dog-rose.
• noun See under Black.
• intransitive verb obsolete To waste away, grow rusty, or be oxidized, as a mineral.
• intransitive verb To be or become diseased, or as if diseased, with canker; to grow corrupt; to become venomous.
• transitive verb To affect as a canker; to eat away; to corrode; to consume.
• transitive verb To infect or pollute; to corrupt.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany A plant disease marked by gradual decay.
• noun A corroding or sloughing ulcer; especially a spreading gangrenous ulcer or collection of ulcers in or about the mouth.
• noun Anything which corrodes, corrupts, or destroys.
• noun A kind of wild, worthless rose; the dog rose.
• noun 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.
• noun An avian disease affecting doves, poultry, parrots but also birds of prey caused by Trichomonas gallinae
• verb transitive To affect as a canker; to eat away; to corrode; to consume.
• verb transitive To infect or pollute; to corrupt.
• verb intransitive To waste away, grow rusty, or be oxidized, as a mineral.
• verb To be or become diseased, or as if diseased, with canker; to grow corrupt; to become venomous.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an ulceration (especially of the lips or lining of the mouth)
• noun a pernicious and malign influence that is hard to get rid of
• verb infect with a canker
• verb become infected with a canker