The Collaborative International Dictionary of English v.0.48:

Appendix \Ap*pen"dix\, n.; pl. E. Appendixes, L. Appendices.
   [L. appendix, -dicis, fr. appendere. See Append.]
   1. Something appended or added; an appendage, adjunct, or
      concomitant.
      [1913 Webster]

            Normandy became an appendix to England. --Sir M.
                                                  Hale.
      [1913 Webster]

   2. Any literary matter added to a book, but not necessarily
      essential to its completeness, and thus distinguished from
      supplement, which is intended to supply deficiencies and
      correct inaccuracies.
      [1913 Webster]

   3. (Anatomy) The vermiform appendix.
      [Webster 1913 Suppl.]

   Syn: See Supplement.
        [1913 Webster]

WordNet (r) 3.0 (2006):

appendix
    n 1: supplementary material that is collected and appended at
         the back of a book
    2: a vestigial process that extends from the lower end of the
       cecum and that resembles a small pouch [syn: appendix,
       vermiform appendix, vermiform process, cecal appendage]