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]