rubeola vs contagious disease

rubeola and contagious disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
rubeola	Yes	No	No	No
contagious disease	Yes	No	No	No

As nouns, contagious disease is a hypernym of rubeola; that is, contagious disease is a word with a broader meaning than rubeola:

rubeola: an acute and highly contagious viral disease marked by distinct red spots followed by a rash; occurs primarily in children
contagious disease: any disease easily transmitted by contact

Other hypernyms of rubeola include contagion.

rubeola (noun)	contagious disease (noun)
an acute and highly contagious viral disease marked by distinct red spots followed by a rash; occurs primarily in children	any disease easily transmitted by contact