roseola vs hives

roseola and hives both are nouns.

Word	Noun	Adjective	Verb	Adverb
roseola	Yes	No	No	No
hives	Yes	No	No	No

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

roseola: any red eruption of the skin
hives: an itchy skin eruption characterized by weals with pale interiors and well-defined red margins; usually the result of an allergic response to insect bites or food or drugs

Other hyponyms of roseola include heat rash, miliaria, prickly heat, nettle rash, urticaria, urtication.

roseola (noun)	hives (noun)
any red eruption of the skin	an itchy skin eruption characterized by weals with pale interiors and well-defined red margins; usually the result of an allergic response to insect bites or food or drugs