United Kingdom vs kingdom

United Kingdom and kingdom both are nouns.

Word	Noun	Adjective	Verb	Adverb
United Kingdom	Yes	No	No	No
kingdom	Yes	No	No	No

United Kingdom (noun)	kingdom (noun)
a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom	a basic group of natural objects
	a monarchy with a king or queen as head of state
	the highest taxonomic group into which organisms are grouped; one of five biological categories: Monera or Protoctista or Plantae or Fungi or Animalia
	the domain ruled by a king or queen
	a country with a king as head of state
	a domain in which something is dominant