Definitions of cereal:

• noun:   a breakfast food prepared from grain
• noun:   grass whose starchy grains are used as food: wheat; rice; rye; oats; maize; buckwheat; millet
• noun:   foodstuff prepared from the starchy grains of cereal grasses
• adjective:   made of grain or relating to grain or the plants that produce it

  Example: "A cereal beverage"