Nile snakes (4)
I believe the answer is:
asps
'nile snakes' 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 "Deadly snakes" , "Poplars" , "native Africans?" , "Cleopatra's snakes" , "Small venomous snakes" .)