USA vs MD

USA and MD both are nouns.

Word	Noun	Adjective	Verb	Adverb
USA	Yes	No	No	No
MD	Yes	No	No	No

USA (noun)	MD (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	a doctor's degree in medicine
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 Mid-Atlantic state; one of the original 13 colonies, with capital Annapolis
	a licensed medical practitioner