Monkshood
I believe the answer is:
'monkshood' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aconite that I've seen before include "potential killer" , "Yellow-flowered plant" , "Poisonous flowering plant" , "Flower, for example monkshood or wolfsbane" , "Spring flower - poison" .)