The Collaborative International Dictionary of English v.0.48:

Commemoration \Com*mem`o*ra"tion\, n. [L. commemoratio.]
   1. The act of commemorating; an observance or celebration
      designed to honor the memory of some person or event.
      [1913 Webster]

            This sacrament was designed to be a standing
            commemoration of the death and passion of our Lord.
                                                  --Abp.
                                                  Tillotson.
      [1913 Webster]

            The commonwealth which . . . chooses the most
            flagrant act of murderous regicide treason for a
            feast of eternal commemoration.       --Burke.
      [1913 Webster]

   2. Whatever serves the purpose of commemorating; a memorial.
      [1913 Webster]

   Commemoration day, at the University of Oxford, Eng., an
      annual observance or ceremony in honor of the benefactors
      of the University, at which time honorary degrees are
      conferred.
      [1913 Webster]

WordNet (r) 3.0 (2006):

commemoration
    n 1: a ceremony to honor the memory of someone or something
         [syn: commemoration, memorialization,
         memorialisation]
    2: a recognition of meritorious service [syn: memorial,
       commemoration, remembrance]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "commemoration":
   anniversaries, anniversary, annual holiday, bicentenary,
   bicentennial, biennial, birthday, bissextile day, celebrating,
   celebration, centenary, centennial, ceremony, decennial,
   diamond jubilee, dressing ship, fanfare, fanfaronade, favor,
   festivity, flourish of trumpets, golden wedding anniversary,
   holiday, holy days, immovable feast, jubilee, keepsake, leap year,
   marking the occasion, memento, memento mori, memorabilia, memorial,
   memorialization, memorials, memories, memory, name day, natal day,
   observance, octennial, ovation, quadrennial, quasquicentennial,
   quincentenary, quincentennial, quinquennial, rejoicing, relic,
   religious rites, remembrance, remembrancer, revel, rite,
   ritual observance, salute, salvo, septennial, sesquicentennial,
   sextennial, silver wedding anniversary, solemn observance,
   solemnization, souvenir, tercentenary, tercentennial, testimonial,
   testimonial banquet, testimonial dinner, toast, token,
   token of remembrance, tribute, tricennial, triennial, triumph,
   trophy, wedding anniversary