U.S. vs mestiza

U.S. and mestiza both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
mestiza	Yes	No	No	No

U.S. (noun)	mestiza (noun)
the executive and legislative and judicial branches of the federal government of the United States	a woman of mixed racial ancestry (especially mixed European and Native American ancestry)
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