Mull, island, 351 sq mi (909 sq km), Argyll and Bute, NW Scotland, largest island of the Inner Hebrides, separated from the mainland by the Sound of Mull and the Firth of Lorn. The land is mountainous, rising from the deeply indented coast line to 3,169 ft (966 m) at Ben More. Mull has gardens and farms. Tobermory, a summer resort, is the chief town. Several medieval castles still stand.