eldest

A custom, as in some ancient boroughs, by which lands and tenements descend to the youngest son, instead of the eldest; or, if the owner have no issue, to the youngest brother.

formerly, the eldest son of the King of France and direct heir to the throne

(Old Testament) the eldest son of Isaac who would have inherited the covenant that God made with Abraham and that Abraham passed on to Isaac

A prerogative given to the eldest coparcener to choose first after an inheritance is divided.

A title borne by every one of the daughters of the kings of Spain and Portugal, except the eldest.