island vs Shikoku

island and Shikoku both are nouns.

Word	Noun	Adjective	Verb	Adverb
island	Yes	No	No	No
Shikoku	Yes	No	No	No

island (noun)	Shikoku (noun)
a zone or area resembling an island	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 land mass (smaller than a continent) that is surrounded by water