gwen,
The meaning of the word has also been variously explained. The generally accepted meaning is that is given by the Cistercian chronicler Helinandus (d. about 1230), who, under the date of about 717, mentions of a vision, shown to a hermit concerning
the dish used by Our Lord at the Last Supper, and about which the hermit then wrote a Latin book called "Gradale." "Now in French," so Helinandus informs us, "Gradalis or Gradale means a dish (scutella), wide and somewhat deep, in which costly viands are wont to be served to the rich in degrees (gradatim), one morsel after another in different rows. In popular speech it is also called "greal" ...
http://www.newadvent.org/cathen/06719a.htm
Bill
