calcium oxiden. A white, caustic, lumpy powder, CaO, used as a refractory, as a flux, in glassmaking, in waste treatment, in insecticides, as an industrial alkali, and in manufacturing steel, paper, and building materials. Also called calx, lime3, quicklime.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.calcium oxide n (Elements & Compounds) a white crystalline base used in the production of calcium hydroxide and bleaching powder and in the manufacture of glass, paper, and steel. Formula: CaO. Also called: lime, quicklime, calx, burnt lime, calcined lime or fluxing lime Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014