Little Missouri vs river

Little Missouri and river both are nouns.

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

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