1. (Abbr. cal) Any of several approximately equal units of heat, each measured as the quantity of heat required to raise the temperature of 1 gram of water by 1°C from a standard initial temperature, especially from 3.98°C, 14.5°C, or 19.5°C, at 1 atmosphere pressure. Also called gram calorie, small calorie.
2. (Abbr. cal) The unit of heat equal to ¹/₁₀₀ the quantity of heat required to raise the temperature of 1 gram of water from 0 to 100°C at 1 atmosphere pressure. Also called mean calorie.
3. 1. (Abbr. Cal) The unit of heat equal to the amount of heat required to raise the temperature of 1 kilogram of water by 1°C at 1 atmosphere pressure. Also called kilocalorie, kilogram calorie, Also called large calorie.
   2. A unit of energy-producing potential equal to this amount of heat that is contained in food and released upon oxidation by the body. Also called nutritionist's calorie.

[French, from Latin calor, heat. See caloric.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.