Cobra's tooth (4)
I believe the answer is:
fang
'cobra's tooth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fang that I've seen before include "Animal's eyetooth to seize and tear prey" , "Eg, wolf or snake's tooth" , "Long pointed tooth" , "Poisonous tooth" , "nipper" .)