'Heir' definitions:

Definition of 'heir'

noun

A person who is entitled by law or by the terms of a will to inherit the estate of another [syn: heir, inheritor, heritor]

noun

A person who inherits some title or office [syn: successor, heir]

From: GCIDE

Heir \Heir\ ([^a]r), n. [OE. heir, eir, hair, OF. heir, eir, F. hoir, L. heres; of uncertain origin. Cf. Hereditary, Heritage.]
1. One who inherits, or is entitled to succeed to the possession of, any property after the death of its owner; one on whom the law bestows the title or property of another at the death of the latter. [1913 Webster]
I am my father's heir and only son. --Shak. [1913 Webster]
2. One who receives any endowment from an ancestor or relation; as, the heir of one's reputation or virtues. [1913 Webster]
And I his heir in misery alone. --Pope. [1913 Webster]
Heir apparent. (Law.) See under Apparent.
Heir at law, one who, after his ancector's death, has a right to inherit all his intestate estate. --Wharton (Law Dict.).
Heir presumptive, one who, if the ancestor should die immediately, would be his heir, but whose right to the inheritance may be defeated by the birth of a nearer relative, or by some other contingency. [1913 Webster]

From: GCIDE

Heir Under the patriarchs the property of a father was divided among the sons of his legitimate wives (Gen. 21:10; 24:36; 25:5), the eldest son getting a larger portion than the rest. The Mosaic law made specific regulations regarding the transmission of real property, which are given in detail in Deut. 21:17; Num. 27:8; 36:6; 27:9-11. Succession to property was a matter of right and not of favour. Christ is the "heir of all things" (Heb. 1:2; Col. 1:15). Believers are heirs of the "promise," "of righteousness," "of the kingdom," "of the world," "of God," "joint heirs" with Christ (Gal 3:29; Heb. 6:17; 11:7; James 2:5; Rom. 4:13; 8:17).