- duchyA dominion or region ruled by a duke or duchess.
- duxThe top (male or female) academic student in a school, or in a year of school; the top student in a specified academic discipline.
- archduchyThe territory (principality) of an archduke.
- dossilA small roll or plug used to stop a sore, wound, etc.; a pledget.
- Duchy of NormandyA country, a duchy in Europe, now only composed of the Channel Islands in the English Channel; a crown possession of the Monarch of England, since the Conquest of England by William the Conqueror, Duke of Normandy; bureaucratically, it is administered by the UK.
- dux bellorumA war leader or warlord.
- Il DuceThe title which Italian dictator Benito Mussolini assumed during his rule (1922—1945).