Duncan is a Scottish surname.
The Scottish Gaelic name Donncheann or Donnchadh are bynames composed of the elements donn, meaning "brown" or "dark" from Donn a Gaelic God; and chadh, meaning "chief" or "noble".
[1][2][3] In some cases when the surname was used in County Sligo, Ireland, it is an Anglicized form of the Irish Gaelic name MacDonough or Mac Donnchadha and Ó Duinnchinn, meaning "descendant of Donncheann".
The surname Duncan is represented in Scottish Gaelic as MacDhonn.