Bureau of the Census vs bureau

Bureau of the Census and bureau both are nouns.

Word	Noun	Adjective	Verb	Adverb
Bureau of the Census	Yes	No	No	No
bureau	Yes	No	No	No

As nouns, bureau is a hypernym of Bureau of the Census; that is, bureau is a word with a broader meaning than Bureau of the Census:

Bureau of the Census: the bureau of the Commerce Department responsible for taking the census; provides demographic information and analyses about the population of the United States
bureau: an administrative unit of government

Other hypernyms of Bureau of the Census include agency, authority, federal agency, government agency, office.

Bureau of the Census (noun)	bureau (noun)
the bureau of the Commerce Department responsible for taking the census; provides demographic information and analyses about the population of the United States	furniture with drawers for keeping clothes
	an administrative unit of government