Cleopatra's nemesis (3)
I believe the answer is:
'cleopatra's nemesis' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asp that I've seen before include "Snake of the Nile" , "Cleopatra's poisoner" , "creeper" , "Snake found in spa" , "Small poisonous snake" .)