classical music vs serious music

classical music and serious music both are nouns.

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

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

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

Other synonyms of classical music include classical.

classical music (noun)	serious 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