Song of Solomon vs Song of Songs

Song of Solomon and Song of Songs both are nouns.

Word	Noun	Adjective	Verb	Adverb
Song of Solomon	Yes	No	No	No
Song of Songs	Yes	No	No	No

As nouns, Song of Solomon and Song of Songs are synonyms defined as:

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

Other synonyms of Song of Solomon include Canticle of Canticles, Canticles.

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