Where the Duncan name comes from

Duncan comes out of the Scottish Gaelic personal name Donnchadh, whose first element is donn, meaning "brown" or "dark". One reading takes the second element as "chief" or "noble". Another takes it as cath, meaning "battle". Donnchadh was the name of two early saints and two kings of Scotland. In Scotland the surname began as a patronymic, taken from a father's given name.

Ireland gave the name a second, separate root in Ó Duinnchinn, from donn, "brown", and ceann, "head". In County Sligo, Duncan also served as an English form of MacDonough, or Mac Donnchadha. Scottish Gaelic writes the surname as MacDhonn.