OK vs U.S.A.

OK and U.S.A. both are nouns.

Word	Noun	Adjective	Verb	Adverb
OK	Yes	No	No	Yes
U.S.A.	Yes	No	No	No

OK (noun)	U.S.A. (noun)
an endorsement	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
a state in south central United States

OK (adverb)	U.S.A. (adverb)
an expression of agreement normally occurring at the beginning of a sentence