The Collaborative International Dictionary of English v.0.48:

Cork \Cork\ (k[^o]rk), n. [Cf. G., Dan., & Sw. kork, D. kurk;
   all fr. Sp. corcho, fr. L. cortex, corticis, bark, rind. Cf.
   Cortex.]
   1. The outer layer of the bark of the cork tree (Quercus
      Suber), of which stoppers for bottles and casks are made.
      See Cutose.
      [1913 Webster]

   2. A stopper for a bottle or cask, cut out of cork.
      [1913 Webster]

   3. A mass of tabular cells formed in any kind of bark, in
      greater or less abundance.
      [1913 Webster]

   Note: Cork is sometimes used wrongly for calk, calker;
         calkin, a sharp piece of iron on the shoe of a horse or
         ox.
         [1913 Webster]

   Cork jackets, a jacket having thin pieces of cork inclosed
      within canvas, and used to aid in swimming.

   Cork tree (Bot.), the species of oak (Quercus Suber of
      Southern Europe) whose bark furnishes the cork of
      commerce.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cork tree
    n 1: deciduous tree of China and Manchuria having a turpentine
         aroma and handsome compound leaves turning yellow in autumn
         and deeply fissured corky bark [syn: cork tree,
         Phellodendron amurense]
    2: prickly Australian coral tree having soft spongy wood [syn:
       cork tree, Erythrina vespertilio]