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

Moby Thesaurus II by Grady Ward, 1.0:

115 Moby Thesaurus words for "tailpiece":
   accession, accessory, accompaniment, addenda, addendum, additament,
   addition, additive, additory, additum, adjunct, adjuvant,
   afterpart, afterpiece, anacrusis, annex, annexation, appanage,
   appendage, appendant, appurtenance, appurtenant, attachment,
   augment, augmentation, back, back door, back seat, back side,
   bass passage, behind, bourdon, breech, bridge, brush, burden,
   cadence, cauda, caudal appendage, caudation, chorus, coda,
   complement, concomitant, continuation, corollary, cue, development,
   division, dock, exposition, extension, extrapolation, fantail,
   figure, fixture, folderol, harmonic close, heel, hind end,
   hind part, hindhead, increase, increment, interlude, intermezzo,
   introductory phrase, measure, movement, musical phrase,
   musical sentence, occiput, offshoot, ornament, part, passage,
   pendant, period, phrase, pigtail, posterior, postern, queue,
   rattail, rear, rear end, rearward, refrain, reinforcement,
   resolution, response, reverse, ritornello, section, side effect,
   side issue, stanza, statement, stern, strain, stub, supplement,
   tab, tag, tail, tail end, trail, trailer, train, tutti,
   tutti passage, undergirding, variation, verse, wake