Object of knightly quests (5)
I believe the answer is:
grail
'object of knightly quests' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for grail that I've seen before include "Medieval knights sought the Holy . . . . ." , "Holy object of search" , "Fabled holy vessel" , "Holy vessel used at the Last Supper" , "The holy chalice used by Christ at the Last Supper" .)