Canker historically referred to destructive sores or ulcers that slowly spread through tissue. The term appears frequently in older medical and botanical language, describing disease that eats away at living matter. In literature the image of a canker became a powerful metaphor for corruption or moral rot developing unseen within a person or society. Poets often describe jealousy, envy, or guilt as a canker in the heart, emphasising how destructive emotions can quietly erode inner harmony.

Canker historically referred to spreading ulcers or sores, particularly those that slowly destroy surrounding tissue. In poetry the word commonly symbolises corruption, moral decay, or hidden evil that eats away at something beautiful. Shakespeare famously used the term to describe destructive envy or hypocrisy. Because cankers spread gradually, they make effective metaphors for social problems, jealousy, or internal guilt. The word is often linked with imagery of rot, worms, or blighted flowers in literary contexts.