calculus

Concise Oxford English Dictionary © 2008 Oxford University Press:
calculus /ˈkalkjʊləs/

▶noun

• 1 (pl. calculuses) (also infinitesimal calculus) the branch of mathematics concerned with the determination and properties of derivatives and integrals of functions, by methods based on the summation of infinitesimal differences.

  ■ a particular method or system of calculation or reasoning.

• 2 (pl. calculi /-lʌɪ, -liː/) Medicine a concretion of minerals formed in the kidney, gall bladder, or other organ. ■another term for tartar.

– origin C17: from L., lit. ‘small pebble’.