Cairo cobras (4)
I believe the answer is:
asps
'cairo cobras' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asps that I've seen before include "Poplars" , "because of their venom?" , "Small vipers" , "Cleopatra's snakes" , "Small venomous snakes" .)