Thames River vs River Thames

Thames River and River Thames both are nouns.

Word	Noun	Adjective	Verb	Adverb
Thames River	Yes	No	No	No
River Thames	Yes	No	No	No

As nouns, Thames River and River Thames are synonyms defined as:

Thames River and River Thames: the longest river in England; flows eastward through London to the North Sea

Other synonyms of Thames River include Thames.

Thames River (noun)	River Thames (noun)
the longest river in England; flows eastward through London to the North Sea	the longest river in England; flows eastward through London to the North Sea