Western Isles vs Western Islands

Western Isles and Western Islands both are nouns.

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

As nouns, Western Isles and Western Islands are synonyms defined as:

Western Isles and Western Islands: a group of more than 500 islands off the western coast of Scotland

Other synonyms of Western Isles include Hebridean Islands, Hebridean Isles, Hebrides.

Western Isles (noun)	Western Islands (noun)
a group of more than 500 islands off the western coast of Scotland	a group of more than 500 islands off the western coast of Scotland