also: しまもり
noun
island chief; island lord
Refers to the ruler or chief of an island, often in historical or fantasy contexts.
彼は小さな島の島主として、島民をまとめていた。
As the island chief of a small island, he kept the islanders together.
その島主は代々、島の平和を守ってきた。
The island lord has protected the peace of the island for generations.
Alternate form with reading しまもり; less common.
領主 is a more general term for a feudal lord or landowner, while 島主 specifically refers to the ruler of an island.
Compound of 島 (island) and 主 (master, chief). The reading とうしゅ uses the on'yomi of both characters.