tonality vs major key

tonality and major key both are nouns.

Word	Noun	Adjective	Verb	Adverb
tonality	Yes	No	No	No
major key	Yes	No	No	No

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

tonality: any of 24 major or minor diatonic scales that provide the tonal framework for a piece of music
major key: a key whose harmony is based on the major scale

Other hyponyms of tonality include major mode, minor key, minor mode, home key, tonic key.

tonality (noun)	major key (noun)
any of 24 major or minor diatonic scales that provide the tonal framework for a piece of music	a key whose harmony is based on the major scale