Solomon Islands vs archipelago

Solomon Islands and archipelago both are nouns.

Word	Noun	Adjective	Verb	Adverb
Solomon Islands	Yes	No	No	No
archipelago	Yes	No	No	No

Solomon Islands (noun)	archipelago (noun)
the southern Solomon Islands that since 1978 form an independent state in the British Commonwealth	a group of many islands in a large body of water
the northernmost islands are part of Papua New Guinea; the remainder form an independent state within the British Commonwealth