hydrocyaniteMin.|haɪdrəʊˈsaɪənaɪt| [Named 1870, f.Gr. ὕδωρ, ὑδρο- water + κύανος blue: see -ite.] Anhydrous sulphate of copper occurring in pale green crystals, which, when exposed to the air, absorb water and become bright blue. 1875Dana Min.App. ii. 29.