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WordNet
erythema nodosum

n. skin condition characterized by tender red nodules on the shins and legs

Wikipedia
Erythema nodosum

Erythema nodosum (EN) is an inflammatory condition characterised by inflammation of the fat cells under the skin, resulting in tender red nodules or lumps that are usually seen on both shins. It can be caused by a variety of conditions, and typically resolves spontaneously within 30 days. It is common in young people between 12–20 years of age.