Pearl River vs river

Pearl River and river both are nouns.

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

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