The cup or plate used by Christ at the Last Supper. Variant definitions include a dish with some kind of supernatural properties, which made its first appearance in the Conte du Graal of Chretien de Troyes. Later it was identified as the chalice used at the Last Supper; also the dish of the paschal lamb or the basin used by Pilate when he washed his hands. A further suggestion had the grail as the container in which Joseph of Arimathea caught the blood of Christ on the Cross. [?< Lat. gradalis = dish]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.