Artist's drink, something bitter (7)
I believe the answer is:
chagall
'artist's' is the definition.
(painter Marc Chagall)
'drink something bitter' is the wordplay.
'drink' becomes 'cha' (cha can mean tea).
'something bitter' becomes 'gall' (gall can mean bile, a bitter substance).
'cha'+'gall'='CHAGALL'
(Other definitions for chagall that I've seen before include "Marc --, Russian-French artist" , "Marc -, twentieth century Russian-born French artist" , "Russian-born painter" , "Marc --, Russian artist" , "He painted" .)