Mix a tonic noted for its deadly properties (7)
I believe the answer is:
aconite
'its deadly properties' is the definition.
I can't tell whether this defines the answer.
'mix a tonic noted' is the wordplay.
'mix' indicates an anagram.
'noted' becomes 'e' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'tonic'='atonic'
'atonic' is an anagram of 'aconit'.
'aconit'+'e'='ACONITE'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for aconite that I've seen before include "Yellow-flowered plant" , "Spring flower - poison" , "Poisonous flowering plant" , "Flower, for example monkshood or wolfsbane" , "potential killer" .)