Old Testament vs Song of Songs

Old Testament and Song of Songs both are nouns.

Word	Noun	Adjective	Verb	Adverb
Old Testament	Yes	No	No	No
Song of Songs	Yes	No	No	No

Old Testament (noun)	Song of Songs (noun)
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	an Old Testament book consisting of a collection of love poems traditionally attributed to Solomon but actually written much later