prayer vs Mass

prayer and Mass both are nouns.

Word	Noun	Adjective	Verb	Adverb
prayer	Yes	No	No	No
Mass	Yes	No	No	No

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

Other hyponyms of prayer include Agnus Dei, Shema.

prayer (noun)	Mass (noun)
the act of communicating with a deity (especially as a petition or in adoration or contrition or thanksgiving)	(Roman Catholic Church and Protestant Churches) the celebration of the Eucharist
earnest or urgent request	a musical setting for a Mass
a fixed text used in praying	a sequence of prayers constituting the Christian Eucharistic rite
reverent petition to a deity
someone who prays to God