U.S. vs Niobrara River

U.S. and Niobrara River both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
Niobrara River	Yes	No	No	No

U.S. (noun)	Niobrara River (noun)
the executive and legislative and judicial branches of the federal government of the United States	a tributary of the Missouri River
North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776