erythema vs sunburn

erythema and sunburn both are nouns.

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

As nouns, sunburn is a hyponym of erythema; that is, sunburn is a word with a more specific, narrower meaning than erythema:

erythema: abnormal redness of the skin resulting from dilation of blood vessels (as in sunburn or inflammation)
sunburn: redness of the skin caused by exposure to the rays of the sun

Other hyponyms of erythema include erythema multiforme, erythema nodosum, hickey, love bite, erythema solare, windburn.

erythema (noun)	sunburn (noun)
abnormal redness of the skin resulting from dilation of blood vessels (as in sunburn or inflammation)	redness of the skin caused by exposure to the rays of the sun

erythema (verb)	sunburn (verb)
	get a sunburn by overexposure to the sun