ebonite

from WordNet (r) 3.0 (2006)

ebonite
    n 1: a hard nonresilient rubber formed by vulcanizing natural
         rubber [syn: {hard rubber}, {vulcanite}, {ebonite}]

from The Collaborative International Dictionary of English v.0.48

Ebonite \Eb"on*ite\, n. (Chem.)
   A hard, black variety of vulcanite. It may be cut and
   polished, and is used for many small articles, as combs and
   buttons, and for insulating material in electric apparatus.
   [1913 Webster]