serious music vs classical music

serious music and classical music both are nouns.

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

As nouns, serious music and classical music are synonyms defined as:

serious music and classical music: traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste

Other synonyms of serious music include classical.

serious music (noun)	classical music (noun)
traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste	traditional genre of music conforming to an established form and appealing to critical interest and developed musical taste