In Scottish, name Douglas means – From the Gaelic dubhglas meaning dark water, dark stream, or from the dark river. The Scottish Douglas clan had two historical branches: (Black Douglases and Red Douglases.) The lords of these clans figure in Sir Walter Scotts novels.. Other origins for name Douglas include – Scottish, Irish, Celtic, Irish, English. Name Douglas is a unisex name and can be used for a boy or girl name (male or female).