1. a nonmetal that in combination with a metal forms an alloy.
  2. an element that has both metallic and nonmetallic properties, as arsenic, silicon, or boron.
  1. of or relating to a metalloid.
  2. resembling both a metal and a nonmetal.

Origin of metalloid

First recorded in 1825–35; metall- + -oid Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for metalloid


  1. a nonmetallic element, such as arsenic or silicon, that has some of the properties of a metal
adjective Also: metalloidal (ˌmɛtəˈlɔɪdəl)
  1. of or being a metalloid
  2. resembling a metal
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

metalloid in Science


  1. 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.
  2. A nonmetallic element, such as carbon, that can form alloys with metals.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.