Douglas, occasionally spelt Douglass, is a Scottish surname. It is thought to derive from the Scottish Gaelic dubh glas, meaning "black stream". There are numerous places in Scotland from which the surname is derived. The surname has developed into the given name Douglas. Douglas is a habitational name, which could be derived from any of the many places so-named. While there are numerous places with this name in Scotland, it is thought, in most cases, to refer to Douglas, South Lanarkshire, the location of Douglas Castle, the chief stronghold of the Lords of Douglas.