calorie

Concise Oxford English Dictionary © 2008 Oxford University Press:
calorie/ˈkaləri/

▶noun (pl. calories)

• 1 (also small calorie) the energy needed to raise the temperature of 1 gram of water through 1°C (now usually defined as 4.1868 joules).

• 2 (also large calorie) the energy needed to raise the temperature of 1 kilogram of water through 1°C, equal to one thousand small calories and often used to measure the energy value of foods.

– origin C19: from Fr., from L. calor ‘heat’ + -ie (see -y3).