Duncan is a Scottish surname. The Scottish Gaelic name Donncheann or Donnchadh are bynames composed of the elements donn, meaning "dark or dark-haired man" or "chieftain"; and cath, meaning "battle", together meaning "dark-haired or dark warrior". [1] Another opinion is that the Gaelic Donnchadh is composed of the elements donn, meaning "brown"; and chadh, meaning "chief" or "noble". [2] [3] [4] 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.