Stories We Like: A Guide to the Comma
1660s, from Latin calculus "reckoning, account," originally "pebble used as a reckoning counter," diminutive of calx (genitive calcis) "limestone" (see chalk (n.)). Modern mathematical sense is a shortening of differential calculus. Also used from 1732 to mean kidney stones, etc., then generally for "concretion occurring accidentally in the animal body," such as dental plaque. Related: Calculous (adj.).
calculus cal·cu·lus (kāl'kyə-ləs)
n. pl. cal·cu·lus·es or cal·cu·li (-lī')
An abnormal concretion in the body, usually formed of mineral salts and most commonly found in the gallbladder, kidney, or urinary bladder. Also called stone.
Plural calculi (kāl'kyə-lī') or calculuses