archipelago vs Western Isles

archipelago and Western Isles both are nouns.

Word	Noun	Adjective	Verb	Adverb
archipelago	Yes	No	No	No
Western Isles	Yes	No	No	No

archipelago (noun)	Western Isles (noun)
a group of many islands in a large body of water	a group of more than 500 islands off the western coast of Scotland