Japanese Islands vs Shikoku

Japanese Islands and Shikoku both are nouns.

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

Japanese Islands (noun)	Shikoku (noun)
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	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