Whom Jason jilted (5)
I believe the answer is:
medea
'whom jason jilted' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for medea that I've seen before include "Tragedy by Euripides" , "Tragic heroine" , "Jason's sorceress" , "Mythical wife who helped Jason get the Golden Fleece" , "Greek princess who helped Jason get the Golden Fleece" .)