religious music vs Mass

religious music and Mass both are nouns.

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

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

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

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

religious 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