U.S.A. vs OK

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

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

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

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