Meanings
-
1
noun
historical chemistry: iron(II) sulfate, a green crystalline compound used in dyes, inks, tanning, and other processes
The workshop combined copperas with tannin to produce black ink.
Thesaurus
Etymology
From Middle English coperas, through Old French coperose from Medieval Latin cuperosa, a name for metallic sulfates. Despite its modern spelling, copperas usually meant green vitriol, or iron(II) sulfate, rather than a copper compound.