Thames vs River Thames

Thames and River Thames both are nouns.

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

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

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

Other synonyms of Thames include Thames River.

Thames (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