Толковый словарь английского языка Oxford English Reference - regulus

n. (pl. reguluses or reguli) Chem. 1 the purer or metallic part of a mineral that separates by sinking on reduction. 2 an impure metallic product formed during the smelting of various ores. Derivatives reguline adj. Etymology: L, dimin. of rex regis king: orig. of a metallic form of antimony, so called because of its readiness to combine with gold