Foreign Service vs bureau

Foreign Service and bureau both are nouns.

Word	Noun	Adjective	Verb	Adverb
Foreign Service	Yes	No	No	No
bureau	Yes	No	No	No

As nouns, bureau is a hypernym of Foreign Service; that is, bureau is a word with a broader meaning than Foreign Service:

Foreign Service: the part of the State Department that supplies diplomats for the United States embassies and consulates around the world
bureau: an administrative unit of government

Other hypernyms of Foreign Service include agency, authority, federal agency, government agency, office.

Foreign Service (noun)	bureau (noun)
the part of the State Department that supplies diplomats for the United States embassies and consulates around the world	furniture with drawers for keeping clothes
	an administrative unit of government