sodium

n. (Na) light malleable silvery-white chemical element (Chemistry)

Sodium (IPA: ) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" (formerly known as ‘group IA’). It has only one stable isotope, 23Na. Sodium was first isolated by Sir Humphry Davy in 1807 by passing an electric current through molten sodium hydroxide. Sodium quickly oxidizes in air and is violently reactive with water, so it must be stored in an inert medium, such as kerosene. Sodium is present in great quantities in the earth's oceans as sodium chloride. It is also a component of many minerals, and it is an essential element for animal life. As such, it is classified as a “dietary inorganic macro-mineral.”
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Sodium /so·di·um/ a chemical element, at. no. 11, symbol Na; the chief cation of extracellular body fluids. [more]Sodium - Community and Resources

Noun
1. a silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite (rock salt)
(synonym) Na, atomic number 11
(hypernym) metallic element, metal
(substance-holonym) seawater, saltwater, brine

n. sodium, active chemical element