(in medieval legend) the cup or platter used by Christ at the Last Supper, and in which Joseph of Arimathea received Christ's blood at the Cross. Quests for it undertaken by medieval knights are described in versions of the Arthurian legends written from the early 13th century onward

a thing that is eagerly pursued or sought after

a cure for the common cold is the medical holy grail

youth culture became the grail of broadcasting