Book of Ruth vs Old Testament

Book of Ruth and Old Testament both are nouns.

Word	Noun	Adjective	Verb	Adverb
Book of Ruth	Yes	No	No	No
Old Testament	Yes	No	No	No

Book of Ruth (noun)	Old Testament (noun)
a book of the Old Testament that tells the story of Ruth who was not an Israelite but who married an Israelite and who stayed with her mother-in-law Naomi after her husband died	the collection of books comprising the sacred scripture of the Hebrews and recording their history as the chosen people; the first half of the Christian Bible