Nile cobra (3)
I believe the answer is:
asp
'nile cobra' 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 "Pa's Cleopatra's killer" , "This Egyptian killer" , "Snake seen in a spa, strangely" , "Cleopatra's supposed nemesis" , "Kind of snake - what a sap" .)