Shikoku vs Japanese Islands

Shikoku and Japanese Islands both are nouns.

Word	Noun	Adjective	Verb	Adverb
Shikoku	Yes	No	No	No
Japanese Islands	Yes	No	No	No

Shikoku (noun)	Japanese Islands (noun)
the smallest of the four main islands of Japan; to the south of Honshu and to the east of Kyushu; separated from Honshu by the Inland Sea; forested and mountainous	a string of more than 3,000 islands to the east of Asia extending 1,300 miles between the Sea of Japan and the western Pacific Ocean