African serpent (3)
(Other definitions for mamba that I've seen before include "Venomous African tree snake" , "One's venomous" , "Deadly African snake" , "Death-dealing African" , "Venomous African snake (often black)" .)
'african serpent' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asp that I've seen before include "Poisonous type" , "Serpent" , "snake appears" , "creeper" , "Venomous snake" .)