French, from the family name of the lords of the Dauphiné, an area of SE France: ultimately a nickname meaning 'dolphin'. In 1349 the future Charles V acquired the lands and the title; when king he ceded them to his eldest son, establishing the practice of passing both title and lands to the Crown Prince.

• dolphin from Late Middle English:

  The name for this small whale goes back through French and Latin to Greek delphin. The form delphin existed in English from the early Middle Ages, but dolphin, from its French equivalent, appeared in the later Middle Ages and finally ousted the earlier word during the 17th century. In another guise the French word entered English as dauphin, the eldest son of the king of France. This is from the family name of the lords of the Dauphiné, an area of southeast France. In 1349 the future Charles V acquired the lands and title of the Dauphiné, and when he became king he ceded both to his eldest son, establishing the pattern of passing them to the crown prince.