river vs Pearl River

river and Pearl River both are nouns.

Word	Noun	Adjective	Verb	Adverb
river	Yes	No	No	No
Pearl River	Yes	No	No	No

river (noun)	Pearl River (noun)
a large natural stream of water (larger than a creek)	a river in Mississippi that flows southward to the Gulf of Mexico
	a river in southeast China that flows into the South China Sea