noun
: any of several white gelatinous or crystalline hydrates Al 2 O 3 . n H 2 O of alumina found in nature, especially in bauxite, or obtained as precipitates by treating solutions of aluminum salts with hydroxides : hydrated alumina ; especially : the trihydrate Al 2 O 3 .3H 2 O or Al(OH) 3 of alumina, regarded as acting both as a weak base and as a weak acid, that occurs as gibbsite and is used chiefly in ceramics, in pigments, and as a reinforcing agent for rubber