The Collaborative International Dictionary of English v.0.48:

Nonmetal \Non"met`al\, n. (Chem.)
   Any one of the set of elements which, as contrasted with the
   metals, possess, produce, or receive, acid rather than basic
   properties; a metalloid; as, oxygen, sulphur, and chlorine
   are nonmetals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nonmetal
    adj 1: not containing or resembling or characteristic of a
           metal; "nonmetallic elements" [syn: nonmetallic,
           nonmetal] [ant: metal(a), metallic]
    n 1: a chemical element lacking typical metallic properties