Isaac Newton and Gottfried Leibniz invented calculus in the mid-seventeenth century. Newton gave it the very tedious name "the science of fluents and fluxions" and Leibniz was the one who gave it its modern name- it's not surprising that Newton's name didn't stick. Leibniz borrowed the word from Latin, where it referred to "a pebble used for counting", with a connection of solving mathematical problems. Because many of these pebbles were made out of limestone, we can further trace this back to the Latin word for "limestone", calx (making it related to words as diverse as causeway, recalcitrant, calcium, and chalk). This is from Greek khalix, also meaning "pebble" but nothing to do with counting this time. Origins of this are surprisingly obscure. It might be from a Proto-Indo-European word meaning "to break up", or it might have a non-IE Pre-Greek origin. Hopefully future resources will shed some light on that. As for now, it's all Greek to us.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.