prayerbook vs breviary

prayerbook and breviary both are nouns.

Word	Noun	Adjective	Verb	Adverb
prayerbook	Yes	No	No	No
breviary	Yes	No	No	No

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

prayerbook: a book containing prayers
breviary: (Roman Catholic Church) a book of prayers to be recited daily by certain priests and members of religious orders

Other hyponyms of prayerbook include missal, Book of Psalms, Psalter.

prayerbook (noun)	breviary (noun)
a book containing prayers	(Roman Catholic Church) a book of prayers to be recited daily by certain priests and members of religious orders