Meaning

noun a hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body

noun an incrustation that forms on the teeth and gums

noun the branch of mathematics that is concerned with limits and with the differentiation and integration of functions

origin* Borrowed from Latin calculus (“a pebble or stone used as reckoning counters in abacus”), diminutive of calx (“limestone”) + -ulus. * Mathematical topic is from differential calculus.

Etymology from Wiktionary, CC BY-SA 3.0