What is "dooncastle"

Dooncastle is a townland in the Parish of Aughagower and Barony of Burrishoole. It is bordered to the West by the townland of Derrygorman in the Parish of Westport.To the north it is bordered by the townland of Sheean in the Parish of Islandeady.It is bordered by the following townlands in the Parish of Aughagower: to the southwest, Meneen; to the south, Knockroosky; to the east, Cushinkeel; to the northeast, Doon.
In this townland are the remnants of Doon Castle, a former stronghold of the McPhilpin clan.