prayer book vs missal

prayer book and missal both are nouns.

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

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

prayer book: a book containing prayers
missal: (Roman Catholic Church) a book containing all the prayers and responses needed to celebrate Mass throughout the year

Other hyponyms of prayer book include breviary, Book of Psalms, Psalter.

prayer book (noun)	missal (noun)
a book containing prayers	(Roman Catholic Church) a book containing all the prayers and responses needed to celebrate Mass throughout the year