formerly, the metallic base of a fixed alkali, or alkaline earth; -- applied by sir h. davy to sodium, potassium, and some other metallic substances whose metallic character was supposed to be not well defined.-now, one of several elementary substances which in the free state are unlike metals, and whose compounds possess or produce acid, rather than basic, properties; a nonmetal; as, boron, carbon, phosphorus, nitrogen, oxygen, sulphur, chlorine, bromine, etc., are metalloids.-having the appearance of a metal.-having the properties of a nonmetal; nonmetallic; acid; negative.