calculous / calculus are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
calculous: (adjective) relating to or caused by or having a calculus or calculi.
calculus: (noun) a hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body. (noun) the branch of mathematics that is concerned with limits and with the differentiation and integration of functions.
calculous: NA
calculus: k·AE·l·k·y·ah·l·ah·s
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)