Song of Songs vs Song of Solomon

Song of Songs and Song of Solomon both are nouns.

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

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

Song of Songs and Song of Solomon: 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 Songs include Canticle of Canticles, Canticles.

Song of Songs (noun)	Song of Solomon (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