From The Collaborative International Dictionary of English v.0.48 [gcide]:
Calcium \Cal"ci*um\ (k[a^]l"s[i^]*[u^]m), n. [NL., from L. calx,
calcis, lime; cf F. calcium. See Calx.] (Chem.)
An elementary substance; a metal which combined with oxygen
forms lime. It is of a pale yellow color, tenacious, and
malleable. It is a member of the alkaline earth group of
elements. Atomic weight 40. Symbol Ca.
[1913 Webster]
Note: Calcium is widely and abundantly disseminated, as in
its compounds calcium carbonate or limestone, calcium
sulphate or gypsum, calcium fluoride or fluor spar,
calcium phosphate or apatite.
[1913 Webster]
Calcium light, an intense light produced by the
incandescence of a stick or ball of lime in the flame of a
combination of oxygen and hydrogen gases, or of oxygen and
coal gas; -- called also Drummond light and {lime
light}.
[1913 Webster +PJC]
From WordNet (r) 3.0 (2006) [wn]:
calcium
n 1: a white metallic element that burns with a brilliant light;
the fifth most abundant element in the earth's crust; an
important component of most plants and animals [syn:
calcium, Ca, atomic number 20]