Pentagon vs The Pentagon

Pentagon and The Pentagon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Pentagon	Yes	No	No	No
The Pentagon	Yes	No	No	No

As nouns, Pentagon and The Pentagon are synonyms defined as:

Pentagon and The Pentagon: a government building with five sides that serves as the headquarters of the United States Department of Defense

Pentagon (noun)	The Pentagon (noun)
a government building with five sides that serves as the headquarters of the United States Department of Defense	a government building with five sides that serves as the headquarters of the United States Department of Defense
the United States military establishment