Juliet's cousin (6)
I believe the answer is:
tybalt
'juliet's cousin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tybalt that I've seen before include "He hates, fights, Romeo" , "Killer of Mercutio (R&J)" , "Capulet's duelling kinsman" , "killer of Montague" .)