African tree snake (5)
I believe the answer is:
mamba
'african tree snake' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mamba that I've seen before include "Venomous Afr. snake" , "Deadly creature" , "Poisonous creature" , "Deadly African snake" , "Venomous snake; rhymes with dance" .)