Anglicized form of the Scottish surname Dubhghlas, meaning "dark river" from Gaelic dubh "dark" and glais "water, river" (an archaic word related to glas "grey, green"). Douglas was originally a place name (for example, a tributary of the River Clyde), which then became a Scottish clan name borne by a powerful line of earls. It has been used as a given name since the 16th century.