Army vs Defense Department

Army and Defense Department both are nouns.

Word	Noun	Adjective	Verb	Adverb
Army	Yes	No	No	No
Defense Department	Yes	No	No	No

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