An element that is not a metal but that has some properties of metals. Arsenic, for example, is a metalloid that has the visual appearance of a metal, but is a poor conductor of electricity; metalloids are generally semiconductors. The elements classified as metalloids are boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. Metalloids can be viewed as a diagonal section on the Period Table, separating metals from nonmetals.
A nonmetallic element, such as carbon, that can form alloys with metals.