large calorie food calorie A unit of energy widely used in nutrition, equivalent to the amount of heat needed to cause one kilogram of water to rise in temperature by one degree Celsius. cal kcal kilocalorie big calorie calorie large calorie based unit large calorie food calorie A unit of energy widely used in nutrition, equivalent to the amount of heat needed to cause one kilogram of water to rise in temperature by one degree Celsius. cal kcal kilocalorie big calorie calorie