prayer book vs breviary

prayer book and breviary both are nouns.

Word	Noun	Adjective	Verb	Adverb
prayer book	Yes	No	No	No
breviary	Yes	No	No	No

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

prayer book: 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 prayer book include missal, Book of Psalms, Psalter.

prayer book (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