Duke

A Duke is a fuedal lord of high rank within the continent of Eynor. While a commonly used title across the continent, the different Kingdoms have their own definitions of Duke, so a Duke of one land is not necessarily the equivalent to a Duke of another.

In Tremany

In the Kingdom of Tremany, the title of Duc (unisex) still holds its original definition. A Duc is the hereditary governor of an entire province by Royal appointment, and is the feudal lord of several local Comtes.
The word "Duc" originated early during the occupation of modern Tremany and Ettany by the Great Empire, and has since been adopted into the languages of other regions and adapted onto their local dialects. It is believed to be a slang term originating in the dialect of Getae Province, meaning "duck", possibly in reference to the similarities between a Duc's ceremonial green hood and the plumage of the ubiquitous mallard duck.

In Wexe

In the Kingdom of Wexe, a Duke (male) or Duchess (female) is a high ranking hereditary lord who holds personal ownership over multiple Wexan Shires, or holds the personal vassalage of multiple Eorls. It is primarily a ceremonial title used to communicate a lord's place within Wexe's social hierarchy, and can be gained or lost with changes in social standing and transfers of vassalage.

In Gruumanland

The Kingdom of Gruumanland does not have its own equivalent of a Duke. Instead, the terms "Dukzog" (male) and "Dukzola" (female) are reserved as ceremonial titles for the reigning monarch and their heir.

In Vistilia

The republic states of Vistilia still use the term "Patricci" (unisex), which is close to the original world for provincial governor as used by the Great Empire. The role itself is mostly unchanged as well, except that the Patricci is effectively a sovereign ruler who is elected for life by eligible voters. Exactly who is eligible to vote to elect a Patricci varies from Vistilian state to state.
The slang word "Ducci", borrowed from the Treman word "Duc", is used to refer to a corrupt official or a head of an organised crime family, sometimes themselves a Patricci.

In Lloth

Although the enigmatic Kingdom of Lloth is notoriously static and resistant to change, its denizens were surprisingly quick to adopt the word "Duke" from neighbouring Wexe. What Duke actually means in Lloth, however, is anyone's guess.

Other

Duke of Ash

See: Saint of Yedenna
A derogatory term for the Saint of Yedenna, the spiritual leader of the Yeddic Path, for their alleged role in the infamous burning of the Biblia di Gilio.