(physics) The major stable isotope of calcium, ⁴⁰₂₀Ca, having twenty protons and twenty neutrons; it amounts to almost 97% of the element in nature

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(physics) A minor stable isotope of calcium, ⁴⁴₂₀Ca, having twenty protons and twenty-four neutrons; it amounts to about 2% of the element in nature

(physics) A minor stable isotope of calcium, ⁴²₂₀Ca, having twenty protons and twenty-two neutrons; it amounts to about 0.6% of the element in nature

(physics) A rare stable isotope of calcium, ⁴⁶₂₀Ca, having twenty protons and twenty-six neutrons; it amounts to only 0.004% of the element in nature

(physics) A minor stable isotope of calcium, ⁴³₂₀Ca, having twenty protons and twenty-three neutrons; it amounts to about 0.1% of the element in nature

(physics) A naturally-occurring radioactive isotope of calcium, ⁴⁸₂₀Ca, having twenty protons and twenty-eight neutrons, and a half-life of 4.3x10¹⁹ years

(inorganic chemistry) The calcium salt of hydrochloric acid, CaCl₂; used as a drying agent and to melt ice on roads.

(inorganic chemistry) A colourless or white inorganic compound, CaCO₃, occurring as chalk, limestone, marble etc; reacts with acids to liberate carbon dioxide.

(chemistry) the calcium salt of sorbic acid