1866, from French calorie, from Latin calor (genitive caloris) "heat," from PIE *kle-os-, suffixed form of root *kele- (1) "warm" (cf. Latin calidus "warm," calere "be hot;" Sanskrit carad- "harvest," literally "hot time;" Lithuanian silti "become warm," silus "August;" Old Norse hlær, Old English hleow "warm").
In scientific use, largely replaced 1950 by the joule. As a unit of energy, defined as "heat required to raise 1 gram of water 1 degree Celsius" (the small or gram calorie), but also as "heat required to raise 1 kilogram of water 1 degree Celsius" (the large calorie or kilocalorie).
calorie cal·o·rie (kāl'ə-rē)
n.
A unit of energy-producing potential supplied by food and released upon oxidation by the body, equal to the amount of energy required to raise the temperature of 1 kilogram of water by 1°C at one atmosphere pressure. Also called nutritionist's calorie.
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, large calorie.
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 at 1 atmosphere pressure. Also called gram calorie, small calorie.
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.