Achill (ăk`ĭl) [Irish,=eagle], island, 56 sq mi (145 sq km), Co. Mayo, W Republic of Ireland; the largest island of Ireland. It is connected with the mainland by a bridge over Achill Sound. The rugged island is barren; there is fishing and subsistence farming. Many small villages are resorts; Keel and Doogort are the chief towns. Achill is known for its magnificent cliffs; Slievemore, at the north end, rises to 2,204 ft (672 m).