Rhine River vs Rhein

Rhine River and Rhein both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rhine River	Yes	No	No	No
Rhein	Yes	No	No	No

As nouns, Rhine River and Rhein are synonyms defined as:

Rhine River and Rhein: a major European river carrying more traffic than any other river in the world; flows into the North Sea

Other synonyms of Rhine River include Rhine.

Rhine River (noun)	Rhein (noun)
a major European river carrying more traffic than any other river in the world; flows into the North Sea	a major European river carrying more traffic than any other river in the world; flows into the North Sea