any of the six highly reactive chemical elements in group IIA of the periodic table including, in order of increasing reactivity, beryllium, magnesium, calcium, strontium, barium, and radium: an oxide of any of these metals is called an
See alkaline-earth metal in American Heritage Dictionary 4
noun
Any of a group of metallic elements, especially calcium, strontium, magnesium, and barium, but generally including beryllium and radium. Also called alkaline earth.