Belgium vs Kingdom of Belgium

Belgium and Kingdom of Belgium both are nouns.

Word	Noun	Adjective	Verb	Adverb
Belgium	Yes	No	No	No
Kingdom of Belgium	Yes	No	No	No

As nouns, Belgium and Kingdom of Belgium are synonyms defined as:

Belgium and Kingdom of Belgium: a monarchy in northwestern Europe; headquarters for the European Union and for the North Atlantic Treaty Organization

Other synonyms of Belgium include Belgique.

Belgium (noun)	Kingdom of Belgium (noun)
a monarchy in northwestern Europe; headquarters for the European Union and for the North Atlantic Treaty Organization	a monarchy in northwestern Europe; headquarters for the European Union and for the North Atlantic Treaty Organization