The Collaborative International Dictionary of English v.0.48:

Ceremony \Cer"e*mo*ny\, n.; pl. Ceremonies. [F.
   c['e]r['e]monie, L. caerimonia; perh. akin to E. create and
   from a root signifying to do or make.]
   1. Ar act or series of acts, often of a symbolical character,
      prescribed by law, custom, or authority, in the conduct of
      important matters, as in the performance of religious
      duties, the transaction of affairs of state, and the
      celebration of notable events; as, the ceremony of
      crowning a sovereign; the ceremonies observed in
      consecrating a church; marriage and baptismal ceremonies.
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            According to all the rites of it, and according to
            all the ceremonies thereof shall ye keep it [the
            Passover].                            --Numb. ix. 3
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            Bring her up the high altar, that she may
            The sacred ceremonies there partake.  --Spenser.
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            [The heralds] with awful ceremony
            And trumpet's sound, throughout the host proclaim
            A solemn council.                     --Milton.
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   2. Behavior regulated by strict etiquette; a formal method of
      performing acts of civility; forms of civility prescribed
      by custom or authority.
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            Ceremony was but devised at first
            To set a gloss on . . . hollow welcomes . . .
            But where there is true friendship there needs none.
                                                  --Shak.
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            Al ceremonies are in themselves very silly things;
            but yet a man of the world should know them.
                                                  --Chesterfield.
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   3. A ceremonial symbols; an emblem, as a crown, scepter,
      garland, etc. [Obs.]
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            Disrobe the images,
            If you find them decked with ceremonies.
            . . . Let no images
            Be hung with C[ae]sar's trophies.     --Shak.
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   4. A sign or prodigy; a portent. [Obs.]
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            C[ae]sar, I never stood on ceremonies,
            Yet, now they fright me.              --Shak.
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   Master of ceremonies, an officer who determines the forms
      to be observed, or superintends their observance, on a
      public occasion.

   Not to stand on ceremony, not to be ceremonious; to be
      familiar, outspoken, or bold.
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WordNet (r) 3.0 (2006):

ceremony
    n 1: a formal event performed on a special occasion; "a ceremony
         commemorating Pearl Harbor" [syn: ceremony, ceremonial,
         ceremonial occasion, observance]
    2: any activity that is performed in an especially solemn
       elaborate or formal way; "the ceremony of smelling the cork
       and tasting the wine"; "he makes a ceremony of addressing his
       golf ball"; "he disposed of it without ceremony"
    3: the proper or conventional behavior on some solemn occasion;
       "an inaugural ceremony"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "ceremony":
   amenities, anniversaries, appearances, baccalaureate service,
   buckram, celebrating, celebration, ceremonial, ceremonies,
   ceremoniousness, civilities, commemoration, commencement,
   convention, conventions, convocation, decorum, dignities, dignity,
   dressing ship, duty, elegancies, empty formality, etiquette,
   exercise, exercises, extrinsicality, fanfare, fanfaronade,
   festivity, flourish of trumpets, form, form of worship, formal,
   formalities, formality, formalization, formula, formulary,
   function, gentilities, graces, graduation, graduation exercises,
   gravity, holiday, holy rite, impersonality, inaugural,
   inauguration, initiation, institution, jubilee, liturgy,
   marking the occasion, memorialization, memory, mode of worship,
   motions, mummery, mystery, niceties, obsequies, observance, office,
   order of worship, ordinance, ovation, performance, pomp, pomposity,
   practice, prescribed form, primness, proprieties, protocol,
   rejoicing, religious ceremony, religious rites, remembrance, revel,
   rigidness, rite, rite de passage, rite of passage, rites, ritual,
   ritual observance, rituality, rituals, sacrament, sacramental,
   salute, salvo, service, solemn observance, solemnity,
   solemnization, starchiness, stiffness, stiltedness, stylization,
   testimonial, testimonial banquet, testimonial dinner, toast,
   tribute, triumph, weight