The Collaborative International Dictionary of English v.0.48:

Finisher \Fin"ish*er\, n.
   1. One who finishes, puts an end to, completes, or perfects;
      esp. used in the trades, as in hatting, weaving, etc., for
      the workman who gives a finishing touch to the work, or
      any part of it, and brings it to perfection.
      [1913 Webster]

            O prophet of glad tidings, finisher
            Of utmost hope!                       --Milton.
      [1913 Webster]

   2. Something that gives the finishing touch to, or settles,
      anything. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

finisher
    n 1: (baseball) a relief pitcher who can protect a lead in the
         last inning or two of the game [syn: closer, finisher]
    2: a racing driver who finishes a race
    3: a painter who applies a finishing coat
    4: a worker who performs the last step in a manufacturing
       process
    5: a race car that finishes a race
    6: an animal that wins in a contest of speed

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "finisher":
   KO, capstone, climax, clincher, conclusive argument, copestone,
   crown, crusher, cutter, death stroke, deathblow, end-all, ender,
   final stroke, final touch, finishing stroke, floorer, garmentmaker,
   garmentworker, kayo, kayo punch, knockdown argument, knockout,
   knockout blow, last dab, last stroke, last touch, needleworker,
   quietus, settler, sockdolager, stitcher, stopper