Foam from venomous serpent (6)
I believe the answer is:
mousse
'foam' is the definition.
(I know that mousse is a type of foam)
'from venomous serpent' is the wordplay.
'from' indicates a hidden word.
'MOUSSE' can be found hidden inside 'venomous serpent'.
(Other definitions for mousse that I've seen before include "Frothy creamy substance for styling hair" , "Shock treatment" , "Whipped savoury dish" , "Light creamy dessert, set with gelatin" , "Whipped sweet" .)