Duke

Duke (male) or Duchess (female) was a title of nobility, used among other places, Renavi.

In the late 2250s, Harcourt Fenton Mudd was wanted by the United Federation of Planets for "attempted regicide," attempting to assassinate a duke, though Mudd didn't feel a duke should qualify as "regicide." 

In 2266, Mudd promised Ruth Bonaventure that upon wedding a lithium miner she'd be (as rich as) a duchess. 

Kor and Curzon Dax broke into the Duke's harem on Renavi. Years later in 2375, Kor asked Ezri Dax if she remembered that event, and she laughed, stating "How could I forget? It's one of Curzon's favorite memories..."