Drink additive (3,4)
(Other definitions for ice cube that I've seen before include "Cooling addition to drink" , "Drink cooler" , "Frozen shape in a drink" , "Six-faced frozen cooler" , "Block used in cold drinks" .)
'drink additive?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Another definition for ade that I've seen is " -- Edmondson, comedian".)