Poisonous snakes (4)
I believe the answer is:
asps
'poisonous snakes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asps that I've seen before include "Deadly snakes" , "Pass among snakes" , "Small venomous snakes" , "Pass (anag)" , "Small vipers" .)