a green, crystalline compound, FeSO·7HO, used in dyeing, the making of ink, etc.; copperas
See ferrous sulfate in American Heritage Dictionary 4
A greenish crystalline compound, FeSO4·7H2O, used as a pigment, fertilizer, and feed additive, in sewage and water treatment, and as a medicine in the treatment of iron deficiency. Also called copperas.