U.S. vs western United States

U.S. and western United States both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
western United States	Yes	No	No	No

U.S. (noun)	western United States (noun)
the executive and legislative and judicial branches of the federal government of the United States	the region of the United States lying to the west of the Mississippi 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