Defense vs Defense Department

Defense and Defense Department both are nouns.

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

As nouns, Defense and Defense Department are synonyms defined as:

Defense and Defense Department: the federal department responsible for safeguarding national security of the United States; created in 1947

Other synonyms of Defense include Department of Defense, DoD, United States Department of Defense.

Defense (noun)	Defense Department (noun)
the federal department responsible for safeguarding national security of the United States; created in 1947	the federal department responsible for safeguarding national security of the United States; created in 1947