*peras*

n. [ OE. coperose, F. couperose, fr. (assumed?) L. cuprirosa, equiv. to G. cha`lkanqos, i. e. copper flower, vitriol. See Copper and Rose. ] Green vitriol, or sulphate of iron; a green crystalline substance, of an astringent taste, used in making ink, in dyeing black, as a tonic in medicine, etc. It is made on a large scale by the oxidation of iron pyrites. Called also ferrous sulphate. [ 1913 Webster ]

☞ The term copperas was formerly synonymous with vitriol, and included the green, blue, and white vitriols, or the sulphates of iron, copper, and zinc. [ 1913 Webster ]