I shan't be mixing drink (8)
I believe the answer is:
absinthe
'drink' is the definition.
(absinthe is a kind of drink)
'i shan't be mixing' is the wordplay.
'mixing' indicates an anagram.
'i'+'shant'+'be'='ishantbe'
'ishantbe' anagrammed gives 'ABSINTHE'.
(Other definitions for absinthe that I've seen before include "Green liqueur flavoured with wormwood and anise" , "Green aniseed liqueur" , "Green wormwood drink" , "Liqueur - the basin (anag)" , "French liqueur" .)