river vs Merrimack River

river and Merrimack River both are nouns.

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

river (noun)	Merrimack River (noun)
a large natural stream of water (larger than a creek)	a river that rises in south central New Hampshire and flows through Concord and Manchester into Massachusetts and empties into the Atlantic Ocean