Pit viper (10)
I believe the answer is:
copperhead
'pit viper' is the definition.
(copperhead is a kind of pit viper)
This is the entire clue.
(Other definitions for copperhead that I've seen before include "venomous sort" , "Venomous type" , "Reptile" , "Venomous, reddish-brown American snake" , "Highly venomous US or Australian snake" .)