missal vs prayer book

missal and prayer book both are nouns.

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

As nouns, prayer book is a hypernym of missal; that is, prayer book is a word with a broader meaning than missal:

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

Other hypernyms of missal include prayerbook.

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