cop·per·as 
(kŏpər-əs)
(kŏpər-əs)n.
A green, crystalline heptahydrate mineral of ferrous sulfate, FeSO4·7H2O. Also called green vitriol.
[Middle English coperose, a metallic sulfate, from Old French, from Medieval Latin cuperōsa, probably short for *aqua cuprōsa, copper water, from Late Latin cuprum, copper; see COPPER1.]