The American Heritage® Dictionary of the English Language, 4th Edition
n. A soft, silver-white, highly or explosively reactive metallic element that occurs in nature only in compounds. It is obtained by electrolysis of its common hydroxide and 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 63.65°C; boiling point 774°C; specific gravity 0.862; valence 1. See Table at element.
n. 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.
the GNU version of the Collaborative International Dictionary of English
n. 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).
The Century Dictionary and Cyclopedia
n. 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.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. 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
Word Usage
"They often contain potassium, which aids in hydration."