alkali metalalkali metal
Chem. any of the six highly reactive metals in group IA of the periodic table including, in increasing order of reactivity, lithium, sodium, potassium, rubidium, cesium, and francium
Any of a group of soft, white, low-density, low-melting, highly reactive metallic elements, including lithium, sodium, potassium, rubidium, cesium, and francium.
(plural alkali metals)