Kingdom of Tonga vs Tonga

Kingdom of Tonga and Tonga both are nouns.

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

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

Kingdom of Tonga and Tonga: a monarchy on a Polynesian archipelago in the South Pacific; achieved independence from the United Kingdom in 1970

Other synonyms of Kingdom of Tonga include Friendly Islands.

Kingdom of Tonga (noun)	Tonga (noun)
a monarchy on a Polynesian archipelago in the South Pacific; achieved independence from the United Kingdom in 1970	the language of the Tongan people of south central Africa (Zambia and Rhodesia)
	a monarchy on a Polynesian archipelago in the South Pacific; achieved independence from the United Kingdom in 1970