The Collaborative International Dictionary of English v.0.48:

Initiation \In*i`ti*a"tion\, n. [L. initiatio: cf. F.
   initiation.]
   [1913 Webster]
   1. The act of initiating, or the process of being initiated
      or introduced; as, initiation into a society, into
      business, literature, etc. "The initiation of courses of
      events." --Pope.
      [1913 Webster]

   2. The form or ceremony by which a person is introduced into
      any society; mode of entrance into an organized body;
      especially, the rite of admission into a secret society or
      order.
      [1913 Webster]

            Silence is the first thing that is taught us at our
            initiation into sacred mysteries.     --Broome.
      [1913 Webster]

WordNet (r) 3.0 (2006):

initiation
    n 1: a formal entry into an organization or position or office;
         "his initiation into the club"; "he was ordered to report
         for induction into the army"; "he gave a speech as part of
         his installation into the hall of fame" [syn: initiation,
         induction, installation]
    2: the act of starting something for the first time; introducing
       something new; "she looked forward to her initiation as an
       adult"; "the foundation of a new scientific society" [syn:
       initiation, founding, foundation, institution,
       origination, creation, innovation, introduction,
       instauration]
    3: wisdom as evidenced by the possession of knowledge; "his
       knowledgeability impressed me"; "his dullness was due to lack
       of initiation" [syn: knowledgeability, knowledgeableness,
       initiation]
    4: an act that sets in motion some course of events [syn:
       trigger, induction, initiation]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "initiation":
   abecedarium, abecedary, acceptance, admission, admittance,
   anchorage, and arithmetic, baccalaureate service, baptism,
   beginning, celebration, ceremonial, ceremony, colonization,
   coming out, commencement, convocation, curtain raiser, debut,
   elementary education, elements, embarkation, embarkment,
   empty formality, enlistment, enrollment, entrance, establishment,
   exercise, exercises, first appearance, first steps, fixation,
   floating, flotation, formal, formality, foundation, function,
   graduation, graduation exercises, hornbook, immission, inaugural,
   inaugural address, inauguration, inception, induction,
   installation, installment, instatement, institution, introduction,
   intromission, investiture, launching, liturgy, lodgment,
   maiden speech, mooring, mummery, observance, office, opener,
   ordination, origination, peopling, performance, plantation,
   population, preliminary, primer, propaedeutic, reading,
   religious ceremony, rite, rite de passage, rite of passage, ritual,
   rudiments, service, settlement, settling, solemnity, solemnization,
   unveiling, writing