The Collaborative International Dictionary of English v.0.48:

Tailpiece \Tail"piece`\, n.
   1. A piece at the end; an appendage.
      [1913 Webster]

   2. (Arch.) One of the timbers which tail into a header, in
      floor framing. See Illust. of Header.
      [1913 Webster]

   3. (Print.) An ornament placed at the bottom of a short page
      to fill up the space, or at the end of a book. --Savage.
      [1913 Webster]

   4. A piece of ebony or other material attached to the lower
      end of a violin or similar instrument, to which the
      strings are fastened.
      [1913 Webster]

   5. (Locks) A piece for transmitting motion from the hub of a
      lock to the latch bolt.
      [Webster 1913 Suppl.]

   6. The part of a telescope containing the adjusting device
      for the eyepiece, etc.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

tailpiece
    n 1: appendage added to extend the length of something