potassium

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A soft, silver-white, extremely reactive element that is an alkali metal, is essential to plant and animal cell functions, and occurs in nature only in compounds. It can be obtained by electrolysis of its hydroxide and is found in, or converted to, a wide variety of salts used especially in fertilizers and soaps. Atomic number 19; atomic weight 39.098; melting point 63.5°C; boiling point 759°C; specific gravity 0.86; valence 1. cross-reference: Periodic Table.

from The Century Dictionary.

• noun Chemical symbol, K (for kalium); atomic weight, 39.1. The metallic base of the alkali potash, a substance not occurring uncombined in nature, but in various combinations widely diffused and of the highest importance. See potash.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) An Alkali element, occurring abundantly but always combined, as in the chloride, sulphate, carbonate, or silicate, in the minerals sylvite, kainite, orthoclase, muscovite, etc. Atomic weight 39.0. Symbol K (Kalium).
• noun the salt KMnO4, crystallizing in dark red prisms having a greenish surface color, and dissolving in water with a beautiful purple red color; -- used as an oxidizer and disinfectant. The name chameleon mineral is applied to this salt and also to potassium manganate.
• noun See Cream of tartar, under Cream.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A soft, waxy, silvery reactive metal that is never found unbound in nature; an element (symbol K) with an atomic number of 19 and atomic weight of 39.0983. The symbol is derived from the Latin kalium.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a light soft silver-white metallic element of the alkali metal group; oxidizes rapidly in air and reacts violently with water; is abundant in nature in combined forms occurring in sea water and in carnallite and kainite and sylvite