Drink nearly undiluted drop in vacant solitude
I believe the answer is:
snakebite
'drink' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for snakebite that I've seen before include "could prove lethal?" , "Cider mixed with lager" , "Cider and lager - it could be poisonous" , "We may be poisoned, given this" , "Drink (dangerous if given by 18!)" .)