Puff ____ (snake) (5)
I believe the answer is:
adder
'puff snake' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for adder that I've seen before include "poisoner" , "Venomous sort" , "One creature" , "Britain's only venomous snake" , "exhibit in the reptile house" .)