Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'copperas'ME & OFr coperose < ML coperosium, prob. < *(aqua) cuprosa, lit., copper (water) < L cupreus, of copper