Move off with new poison (5)
I believe the answer is:
venom
'poison' is the definition.
(I know that venom is a type of animal toxin)
'move off with new' is the wordplay.
'off with' indicates an anagram.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'move' with its letters anagrammed with 'n' gives 'VENOM'.
(Other definitions for venom that I've seen before include "Poison - spite" , "Virulence" , "Poison; malice" , "Toxic substance" , "Snake poison" .)