cal·ci·um (k?l?s?-?m)n. Symbol Ca A silvery, moderately hard alkaline-earth metal that constitutes approximately 3.6 percent of the earth’s crust and is a basic component of most animals and plants. It occurs naturally in limestone, gypsum, and fluorite, and its compounds are used to make plaster, quicklime, Portland cement, and metallurgic and electronic materials. Atomic number 20; atomic weight 40.08; melting point 842°C; boiling point 1,484°C; specific gravity 1.54; valence 2. See Periodic Table.[Latin calx, calc-, lime; see calx + -ium.]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 (?kæls??m) n (Elements & Compounds) a malleable silvery-white metallic element of the alkaline earth group; the fifth most abundant element in the earth’s crust (3.6 per cent), occurring esp as forms of calcium carbonate. It is an essential constituent of bones and teeth and is used as a deoxidizer in steel. Symbol: Ca; atomic no: 20; atomic wt: 40.078; valency: 2; relative density: 1.55; melting pt: 842±2°C; boiling pt: 1494°C[C19: from New Latin, from Latin calx lime]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014cal?ci?um (?kæl si ?m) n. a silver-white divalent metal, combined in limestone, chalk, etc., occurring also in animals in bone, shell, etc. Symbol: Ca; at. wt.: 40.08; at. no.: 20; sp. gr.: 1.55 at 20°C. [1808;