heir (n.)

"one who inherits, or has right of inheritance in, the property of another," c. 1300, from Anglo-French heir, Old French oir "heir, successor; heritage, inheritance," from Latin heredem (nominative heres) "heir, heiress" (see heredity). Heir apparent (late 14c.) has the French order of noun-adjective, though it was not originally so written in English. It is the heir of one still alive whose right is clear. After death the heir apparent becomes the heir-at-law. Related: Heir-apparency.