1.
island country, island nation
A country consisting entirely of islands, surrounded by sea. Often used in reference to Japan as an island nation, especially when discussing how geography has shaped its culture and character.
島国 is a compound of 島 (island) + 国 (country). The reading uses rendaku (国 → ぐに).
Cultural note
In Japanese discourse, 島国 frequently appears in discussions about Japan's national character, isolation, and cultural uniqueness. The phrase 島国根性 (island mentality) refers to perceived insular or parochial attitudes.