birthright I. birthright\ˈ ̷ ̷ˌ ̷ ̷\noun : a right, privilege, or possession to which a person is entitled by birth (as an estate or as civil liberty guaranteed under a constitution); especially: the inheritance of the firstborn < to sell his birthright for a mess of pottage > Synonyms:see right II. birth·rightadjective Etymology:birthright, noun : being a member of a group by birth < a birthright Quaker >