The term 'ADD FIZZ TO' can be completed with the crossword solutions CARBONATE (9 letters), AERATE (6 letters), SLOE (4 letters), and FLAT (4 letters). Carbonating a beverage involves adding carbon dioxide to it, which gives it a bubbly texture. Aerating a beverage is similar to carbonating, but instead of adding carbon dioxide, oxygen is added. SLOE is a type of fruit that is used to make liqueurs and other alcoholic beverages. FLAT refers to a beverage that has lost its carbonation or fizz.