Definition of copperas in US English:



  • Green crystals of hydrated ferrous sulfate, especially as an industrial product.

    • ‘Removal of large amounts of ordinary cave sediment may indicate saltpeter or fertilizer mining, while gypsum, copperas, alum, or Epsom salt are usually indicated by crystalline or powdered white, yellow, or green deposits.’
    • ‘An inventory of Okeman's works near Poole in Dorset, dated November 1583, records 55 hogsheads of copperas, along with the equipment for manufacturing alum and copperas.’
    • ‘I cannot argue the case for Deptford copperas before the mid-17th century, but it was clearly a long-standing works when taken over by the Crispe family after the Civil War.’
    • ‘These knobbly, metallic-looking fossils were turned into a mixture of dilute sulphuric acid and dissolved copperas using a dangerous, complicated and highly noxious industrial process.’
    • ‘Other items also were extracted from Tennessee caves in the 19th century, including alum, copperas, Epsom salt, gypsum, and nitrogen enriched soil.’


Late Middle English coperose, from Old French couperose, from medieval Latin cuperosa, literally ‘flower of copper’, from late Latin cuprum (see copper) + rosa ‘rose’, translating Greek khalkanthon.