river vs Little Missouri

river and Little Missouri both are nouns.

Word	Noun	Adjective	Verb	Adverb
river	Yes	No	No	No
Little Missouri	Yes	No	No	No

river (noun)	Little Missouri (noun)
a large natural stream of water (larger than a creek)	a river that rises in northeastern Wyoming and flows through Montana and South Dakota to join the Missouri River in North Dakota