Formerly, the eldest son of the King of France and direct heir to the throne WordNet 3.0 & Open English WordNet

Dauphin of France, originally Dauphin of Viennois, was the title given to the heir apparent to the throne of France from 1350 to 1791, and from 1824 to 1830. Wikipedia

Heir apparent to the French crown Wikipedia Disambiguation

Title given to the heir apparent to the throne of France Wikidata

The eldest son of the king of France. Under the Valois and Bourbon dynasties, the Dauphin of France, generally shortened to Dauphin, was heir apparent to the throne of France. The title derived from the main title of the Dauphin, Dauphin of Viennois. Wiktionary

Eldest son of king of France. Wiktionary (translation)