Source : Webster's Revised Unabridged Dictionary (1913)

Birthright \Birth"right`\, n.
   Any right, privilege, or possession to which a person is
   entitled by birth, such as an estate descendible by law to an
   heir, or civil liberty under a free constitution; esp. the
   rights or inheritance of the first born.

         Lest there be any . . . profane person, as Esau, who
         for one morsel of meat sold his birthright. --Heb. xii.
                                                  16.

Source : WordNet®

birthright
     n 1: a right or privilege that you are entitled to at birth;
          "free public education is the birthright of every
          American child"
     2: an inheritance coming by right of birth (especially by
        primogeniture) [syn: {patrimony}]
     3: personal characteristics that are inherited at birth