Song of Songs vs Old Testament

Song of Songs and Old Testament both are nouns.

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

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