The Collaborative International Dictionary of English v.0.48:

Metalloid \Met"al*loid\, n. [L. metallum metal + -oid: cf. F.
   m['e]tallo["i]de.]
      (a) Formerly, the metallic base of a fixed alkali, or
          alkaline earth; -- applied by Sir Humphrey Davy to
          sodium, potassium, and some other metallic substances
          whose metallic character was supposed to be not well
          defined.
      (b) 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.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Metalloid \Met"al*loid\, a.
   1. Having the appearance of a metal.
      [1913 Webster]

   2. (Chem.) Having the properties of a nonmetal; nonmetallic;
      acid; negative.
      [1913 Webster]

WordNet (r) 3.0 (2006):

metalloid
    adj 1: of or being a nonmetallic element that has some of the
           properties of metal; "arsenic is a metalloid element"