Department of Defense vs USA

Department of Defense and USA both are nouns.

Word	Noun	Adjective	Verb	Adverb
Department of Defense	Yes	No	No	No
USA	Yes	No	No	No

Department of Defense (noun)	USA (noun)
the federal department responsible for safeguarding national security of the United States; created in 1947	the army of the United States of America; the agency that organizes and trains soldiers for land warfare
	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