Forth vs Forth River

Forth and Forth River both are nouns.

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

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

Forth and Forth River: a river in southern Scotland that flows eastward to the Firth of Forth

Forth (noun)	Forth River (noun)
a river in southern Scotland that flows eastward to the Firth of Forth	a river in southern Scotland that flows eastward to the Firth of Forth