U.S. vs Sun Belt

U.S. and Sun Belt both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
Sun Belt	Yes	No	No	No

U.S. (noun)	Sun Belt (noun)
the executive and legislative and judicial branches of the federal government of the United States	states in the south and southwest that have a warm climate and tend to be politically conservative
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