(n)(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; he traded his birthright to his twin brother Jacob for a mess of pottage
‖n.; pl.Thesauri [ L. See Treasure. ] A treasury or storehouse; hence, a repository, especially of knowledge; -- often applied to a comprehensive work, like a dictionary or cyclopedia. [ 1913 Webster ]