Forth River vs Forth

Forth River and Forth both are nouns.

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

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

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

Forth River (noun)	Forth (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