Boyd’s Bible Dictionary:

(inheritor). Eldest son became head of tribe or family with largest share of paternal estate; sons of concubines given presents; daughters, a marriage portion (Gen. 21:10, 14; 24:36; 25:6; 31:14; Judg. 11:2). Real estate apportioned as (Deut. 21:17; Num. 27:4-11).

Concise Bible Dictionary:

This is used in various applications as of one coming into a possession. It is applied to the Lord when He came to Israel seeking fruit. They said in effect, “This is the heir: come let us kill him, and the inheritance shall be ours” (Mark 12:7). Christ is appointed by God to be heir of all things (Heb. 1:2). Believers are by grace made sons through Christ, hence heirs, heirs of God, and joint-heirs with Christ (Rom. 8:17; Gal. 4:7: Compare John 17:22).