rondo vs serious music

rondo and serious music both are nouns.

Word	Noun	Adjective	Verb	Adverb
rondo	Yes	No	No	No
serious music	Yes	No	No	No

As nouns, serious music is a hypernym of rondo; that is, serious music is a word with a broader meaning than rondo:

rondo: a musical form that is often the last movement of a sonata
serious music: traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste

Other hypernyms of rondo include classical, classical music.

rondo (noun)	serious music (noun)
a musical form that is often the last movement of a sonata	traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste