The Collaborative International Dictionary of English v.0.48:

Exposition \Ex`po*si"tion\, n. [L. expositio, fr. exponere,
   expositum: cf. F. exposition. See Expound.]
   1. The act of exposing or laying open; a setting out or
      displaying to public view.
      [1913 Webster]

   2. The act of expounding or of laying open the sense or
      meaning of an author, or a passage; explanation;
      interpretation; the sense put upon a passage; a law, or
      the like, by an interpreter; hence, a work containing
      explanations or interpretations; a commentary.
      [1913 Webster]

            You know the law; your exposition
            Hath been most sound.                 --Shak.
      [1913 Webster]

   3. Situation or position with reference to direction of view
      or accessibility to influence of sun, wind, etc.;
      exposure; as, an easterly exposition; an exposition to the
      sun. [Obs.] --Arbuthnot.
      [1913 Webster]

   4. A public exhibition or show, as of industrial and artistic
      productions; as, the Paris Exposition of 1878. [A
      Gallicism]
      [1913 Webster]

WordNet (r) 3.0 (2006):

exposition
    n 1: a systematic interpretation or explanation (usually
         written) of a specific topic [syn: exposition,
         expounding]
    2: a collection of things (goods or works of art etc.) for
       public display [syn: exhibition, exposition, expo]
    3: an account that sets forth the meaning or intent of a writing
       or discourse; "we would have understood the play better if
       there had been some initial exposition of the background"
    4: (music) the section of a movement (especially in sonata form)
       where the major musical themes first occur

Moby Thesaurus II by Grady Ward, 1.0:

217 Moby Thesaurus words for "exposition":
   allegorization, anacrusis, apocalypse, article, assignment,
   auto show, baring, bass passage, bazaar, boat show, bourdon,
   bridge, burden, cadence, causerie, chalk talk, chorus,
   clarification, coda, commentary, commercial complex, construction,
   cosmorama, cracking, critique, cyclorama, decipherment,
   declaration, decoding, delineation, demonstration,
   demythologization, descant, description, development, diorama,
   disclosing, disclosure, discourse, discovering, discovery,
   discussion, display, disquisition, dissertation, division, editing,
   elucidation, emendation, emporium, enactment, enlightenment,
   enunciation, essay, etude, euhemerism, examination, excursus,
   exegesis, exemplification, exercise, exhibit, exhibition,
   explanation, explication, expo, expose, exposure, expounding, fair,
   feature, figure, first approach, flea fair, flea market, folderol,
   georama, harangue, harmonic close, homework, homily, illumination,
   illustration, instruction, interlude, intermezzo, interpretation,
   introductory phrase, introductory study, laying bare, lecture,
   lecture-demonstration, lesson, light, light show, lucubration,
   manifestation, market, market overt, marketplace, mart, measure,
   memoir, monograph, moral, moral lesson, morality, moralization,
   morceau, movement, musical phrase, musical sentence, myriorama,
   note, object lesson, open market, opening, ornament, ostentation,
   outline, pageant, pageantry, pandect, panorama, paper, parade,
   paragraph, part, passage, patefaction, performance, period,
   phantasmagoria, phrase, piece, plaza, pomp, preachment,
   preliminary study, presentation, presentment, production,
   projection, prolegomenon, psychedelic show, rationale, reason,
   recital, recitation, refrain, removing the veil, representation,
   research paper, resolution, response, retrospective, revealing,
   revealment, revelation, rialto, ritornello, screed, section,
   sermon, set task, shifting scene, shopping center, shopping mall,
   shopping plaza, show, showing, showing up, showup, sight,
   simplification, sketch, skull session, solution, special article,
   spectacle, stage show, stanza, staple, statement, strain,
   street market, stripping, study, survey, tableau, tableau vivant,
   tailpiece, talk, task, teaching, term paper, theme, thesis, tract,
   tractate, trade fair, treatise, treatment, tutti, tutti passage,
   uncloaking, uncovering, unfolding, unfoldment, unlocking,
   unmasking, unveiling, unwrapping, variation, varnishing day,
   vernissage, verse