Western Isles vs archipelago

Western Isles and archipelago both are nouns.

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

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