Legendary cup or platter (5)
I believe the answer is:
grail
(Other definitions for grail that I've seen before include "Round Table Knights sought the Holy ....." , "The holy chalice used by Christ at the Last Supper" , "Chalice used by Jesus at the Last Supper" , "Cherished ambition (sought by the Knights of the Round Table)" , "Holy vessel used at the Last Supper" .)