erythema nodosum vs erythema

erythema nodosum and erythema both are nouns.

Word	Noun	Adjective	Verb	Adverb
erythema nodosum	Yes	No	No	No
erythema	Yes	No	No	No

As nouns, erythema is a hypernym of erythema nodosum; that is, erythema is a word with a broader meaning than erythema nodosum:

erythema nodosum: skin condition characterized by tender red nodules on the shins and legs
erythema: abnormal redness of the skin resulting from dilation of blood vessels (as in sunburn or inflammation)

erythema nodosum (noun)	erythema (noun)
skin condition characterized by tender red nodules on the shins and legs	abnormal redness of the skin resulting from dilation of blood vessels (as in sunburn or inflammation)