major scale vs C major

major scale and C major both are nouns.

Word	Noun	Adjective	Verb	Adverb
major scale	Yes	No	No	No
C major	Yes	No	No	No

As nouns, C major is a hyponym of major scale; that is, C major is a word with a more specific, narrower meaning than major scale:

major scale: a diatonic scale with notes separated by whole tones except for the 3rd and 4th and 7th and 8th
C major: (music) the major scale having no sharps or flats

Other hyponyms of major scale include C major scale, scale of C major.

major scale (noun)	C major (noun)
a diatonic scale with notes separated by whole tones except for the 3rd and 4th and 7th and 8th	(music) the major scale having no sharps or flats