The Collaborative International Dictionary of English v.0.48:

Anniversary \An`ni*ver"sa*ry\, a. [L. anniversarius; annus year
   + vertere, versum, to turn: cf. F. anniversaire.]
   Returning with the year, at a stated time; annual; yearly;
   as, an anniversary feast.
   [1913 Webster]

   Anniversary day (R. C. Ch.). See Anniversary, n., 2.

   Anniversary week, that week in the year in which the annual
      meetings of religious and benevolent societies are held in
      Boston and New York. [Eastern U. S.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Anniversary \An`ni*ver"sa*ry\, n.; pl. Anniversaries. [Cf. F.
   anniversaire.]
   1. The annual return of the day on which any notable event
      took place, or is wont to be celebrated; as, the
      anniversary of the Declaration of Independence.
      [1913 Webster]

   2. (R. C. Ch.) The day on which Mass is said yearly for the
      soul of a deceased person; the commemoration of some
      sacred event, as the dedication of a church or the
      consecration of a pope.
      [1913 Webster]

   3. The celebration which takes place on an anniversary day.
      --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

anniversary
    n 1: the date on which an event occurred in some previous year
         (or the celebration of it) [syn: anniversary, day of
         remembrance]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "anniversary":
   Admission Day, Arbor Day, Armed Forces Day, Armistice Day,
   Army Day, Bastille Day, Colorado Day, Constitution Day,
   Decoration Day, Dewali, Discovery Day, Double Ten, Easter Monday,
   Election Day, Empire Day, Evacuation Day, Flag Day, Foundation Day,
   Fourth of July, Groundhog Day, Halifax Day, Halloween, Holi,
   Ides of March, Kuhio Day, Labor Day, Lenin Memorial Day,
   Loyalty Day, Maryland Day, May Day, Mecklenburg Day, Memorial Day,
   Midsummer Day, National Aviation Day, Navy Day, Nevada Day,
   Pan American Day, Pascua Florida Day, Pioneer Day, Remembrance Day,
   Roosevelt Day, State Day, Texas Independence Day,
   United Nations Day, V-E Day, Victory Day, West Virginia Day,
   Wyoming Day, anniversaries, annual holiday, bicentenary,
   bicentennial, biennial, birthday, bissextile day, celebrating,
   celebration, centenary, centennial, ceremony, commemoration,
   decennial, diamond jubilee, dressing ship, fanfare, fanfaronade,
   festivity, flourish of trumpets, golden wedding anniversary,
   holiday, holy days, immovable feast, jubilee, leap year,
   marking the occasion, memorialization, memory, name day, natal day,
   observance, octennial, ovation, quadrennial, quasquicentennial,
   quincentenary, quincentennial, quinquennial, rejoicing,
   religious rites, remembrance, revel, rite, ritual observance,
   salute, salvo, septennial, sesquicentennial, sextennial,
   silver wedding anniversary, solemn observance, solemnization,
   tercentenary, tercentennial, testimonial, testimonial banquet,
   testimonial dinner, toast, tribute, tricennial, triennial, triumph,
   wedding anniversary