solitary island; isolated island
Refers to an island that is far from other land or stands alone, often with a nuance of remoteness or isolation.
その孤島には人が住んでいない。
No one lives on that solitary island.
The ship wrecked and he washed up on a solitary island.
彼は孤島で一人で暮らしている。
He lives alone on an isolated island.
Tourists were stranded on the isolated island because of the typhoon.
At work, she felt like a solitary island, cut off from everyone else.
無人島 specifically means an uninhabited island, whereas 孤島 focuses on the island's isolation rather than whether people live there.
Compound of 孤 (ko, 'solitary') and 島 (tō, 'island'). The kanji 孤 carries a sense of being alone or orphaned, reinforcing the nuance of isolation.