Merrimack River vs river

Merrimack River and river both are nouns.

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

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