The Last Supper Vessel is referred to as the GRAIL, a 5-letter word. The GRAIL is a legendary object associated with the Christian tradition of the Last Supper. It is said to be the cup used by Jesus at the Last Supper and is believed to have miraculous powers. In medieval literature, the GRAIL was often described as a dish, plate, or stone with miraculous powers. The GRAIL has been a popular subject in literature and art since the 12th century.