Shakespearean killer (3)
I believe the answer is:
asp
'shakespearean killer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asp that I've seen before include "Cleopatra's supposed nemesis" , "Snake seen in a spa, strangely" , "Cleopatra-killing snake" , "Venomous snake" , "Slithery thing" .)