canker

noun

• 1a destructive fungal disease of apple and other trees that results in damage to the bark: cut out lesions on branches caused by canker
• [count noun] an open lesion in plant tissue caused by infection or injury: check trees for cankers
• fungal rot in some fruits and vegetables, e.g. parsnips and tomatoes: canker is this crop’s arch enemy

• 2an ulcerous condition or disease of a human or animal, in particular:
• (also canker sore) North American a small ulcer of the mouth or lips: a remedy for canker sores
• another term for thrush² (sense 2).
• ulceration of the throat and other orifices of birds, typically caused by a protozoal infection:secondary infections of canker and coccidiosis
• inflammation of the ear of a dog, cat, or rabbit, typically caused by a mite infestation.

• 3a malign and corrupting influence that is difficult to eradicate: [in singular]:racism remains a canker at the heart of the nation

verb

• 1 [no object] (of woody plant tissue) become infected with canker: (as noun cankering)we found some cankering of the wood

• 2 (as adjective cankered) infected with a pervasive and corrupting bitterness:he hated her with a cankered, shameful abhorrence