alkali metal

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

• noun Any of a group of soft, white, low-density, low-melting, highly reactive metallic elements, including lithium, sodium, potassium, rubidium, cesium, and francium.

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

• Any one of the univalent metals of group I of the periodic table of the elements, including lithium, sodium, potassium, rubidium, cesium, and francium. The hydroxides of these metals are soluble in water and form strongly basic solutions.

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

• noun inorganic chemistry Any of the soft, light, reactive metals of Group 1 of the periodic table; lithium, sodium, potassium, rubidium, cesium, and francium.

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

• noun any of the monovalent metals of group I of the periodic table (lithium or sodium or potassium or rubidium or cesium or francium)