Frankfurt vs Frankfurt on the Main

Frankfurt and Frankfurt on the Main both are nouns.

Word	Noun	Adjective	Verb	Adverb
Frankfurt	Yes	No	No	No
Frankfurt on the Main	Yes	No	No	No

As nouns, Frankfurt and Frankfurt on the Main are synonyms defined as:

Frankfurt and Frankfurt on the Main: a German city; an industrial and commercial and financial center

Other synonyms of Frankfurt include Frankfort.

Frankfurt (noun)	Frankfurt on the Main (noun)
a German city; an industrial and commercial and financial center	a German city; an industrial and commercial and financial center