n. (pl. calculuses or calculi)
1. Math. a a particular method of calculation or reasoning (calculus of probabilities). b the infinitesimal calculuses of integration or differentiation (see integral calculus, differential calculus).
2 Med. a stone or concretion of minerals formed within the body.
calculous adj. (in sense 2).
Etymology: L, small stone used in reckoning on an abacus