church music vs Mass

church music and Mass both are nouns.

Word	Noun	Adjective	Verb	Adverb
church music	Yes	No	No	No
Mass	Yes	No	No	No

As nouns, Mass is a hyponym of church music; that is, Mass is a word with a more specific, narrower meaning than church music:

church music: genre of music composed for performance as part of religious ceremonies
Mass: a musical setting for a Mass

Other hyponyms of church music include antiphon, antiphony, processional, prosodion, antiphonal, antiphonary, religious song.

church music (noun)	Mass (noun)
genre of music composed for performance as part of religious ceremonies	(Roman Catholic Church and Protestant Churches) the celebration of the Eucharist
	a musical setting for a Mass
	a sequence of prayers constituting the Christian Eucharistic rite