calculous / calculus [ˈkælkjʊləs]
calculous (can also be spelled calculus when used as a noun but not when used as an adjective) – n. – stone-like concretions or a mineral formation especially where it doesn’t belong; adj. – the formation of such concretions
calculus (no alternate spelling) – n. – a branch of mathematics that deals with the finding and properties of derivatives and integrals of functions, by methods originally based on the summation of infinitesimal differences.