The Collaborative International Dictionary of English v.0.48:

Annunciation \An*nun`ci*a"tion\ (?; 277), n. [L. annuntiatio:
   cf. F. annonciation.]
   1. The act of announcing; announcement; proclamation; as, the
      annunciation of peace.
      [1913 Webster]

   2. (Eccl.)
      (a) The announcement of the incarnation, made by the angel
          Gabriel to the Virgin Mary.
      (b) The festival celebrated (March 25th) by the Church of
          England, of Rome, etc., in memory of the angel's
          announcement, on that day; Lady Day.
          [1913 Webster]

WordNet (r) 3.0 (2006):

Annunciation
    n 1: a festival commemorating the announcement of the
         Incarnation by the angel Gabriel to the Virgin Mary; a
         quarter day in England, Wales, and Ireland [syn:
         Annunciation, Lady Day, Annunciation Day, March 25]
    2: (Christianity) the announcement to the Virgin Mary by the
       angel Gabriel of the incarnation of Christ
    3: a formal public statement; "the government made an
       announcement about changes in the drug war"; "a declaration
       of independence" [syn: announcement, proclamation,
       annunciation, declaration]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "annunciation":
   affirmance, affirmation, allegation, announcement, assertion,
   asseveration, averment, avouchment, avowal, bulletin board,
   circular, communique, conclusion, creed, declaration, dictum,
   edict, encyclical, enunciation, ipse dixit, manifesto, notice,
   notification, position, position paper, positive declaration,
   predicate, predication, proclamation, profession, program,
   programma, pronouncement, pronunciamento, proposition, protest,
   protestation, public notice, report, say, say-so, saying, stance,
   stand, statement, ukase, utterance, vouch, white book, white paper,
   word