| a salt, copper sulfate, CuSO4·5H2O, occurring naturally as large transparent, deep-blue triclinic crystals, appearing in its anhydrous state as a white powder: used chiefly as a mordant, insecticide, fungicide, and in engraving. |
| blue vitriol n. A blue, crystalline hydrous solution of copper sulfate, CuSO4·5H2O, one of the most important industrial copper salts, used in insecticides, germicides, and hair dyes and in the processing of leather and textiles. |
