cal·ci·um

[kal-see-uhm]
noun Chemistry, Biology.
a silver-white divalent metal, occurring combined in limestone, chalk, gypsum, etc., occurring also in vertebrates and other animals, as a component of bone, skeletal mass, shell, etc., and as a necessary element in nerve conduction, heartbeat, muscle contraction, and many other physiological functions. Symbol: Ca; atomic weight: 40.08; atomic number: 20; specific gravity: 1.55 at 20°C.
Origin:
1800–10; calc- + -ium

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Based on the Random House Dictionary, © Random House, Inc. 2013.
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00:10
Calcium is always a great word to know.
So is hyaline cartilage. Does it mean:
the typical, translucent form of cartilage, containing little fibrous tissue.
something that has ossified; a bony formation
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Collins
World English Dictionary
calcium (ˈkælsɪəm) [Click for IPA pronunciation guide]
 
—n
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 & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Etymonline
Word Origin & History

calcium
coined 1808 by Sir Humphry Davy from L. calx (gen. calcis) "limestone" (see chalk).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

calcium cal·ci·um (kāl'sē-əm)
n.
Symbol Ca
A soft metallic element that is a basic component of animals and plants and constitutes [approx] 3 percent of Earth's crust. It occurs naturally in limestone, gypsum, and fluorite. Atomic number 20; atomic weight 40.08; melting point 842°C; boiling point 1,484°C; specific gravity 1.55; valence 2.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
calcium   (kāl'sē-əm)  Pronunciation Key 
Symbol Ca
A silvery-white, moderately hard metallic element of the alkaline-earth group that occurs in limestone and gypsum. It is a basic component of leaves, bones, teeth, and shells, and is essential for the normal growth and development of most animals and plants. Calcium is used to make plaster, cement, and alloys. Atomic number 20; atomic weight 40.08; melting point 842 to 848°C; boiling point 1,487°C; specific gravity 1.55; valence 2. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
In reefs, all the builders die: the bricks are calcium carbonate shells.
They need more calcium and vitamins with advancing age, and many do not get
  them.
Beta blockers and calcium channel blockers did not work.
Shelled creatures, whose calcium-carbonate-rich armour tends to dissolve in
  acid, suddenly became rare.
Images for calcium
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