The Collaborative International Dictionary of English v.0.48:

Manifestation \Man`i*fes*ta"tion\, n. [L. manifestatio: cf. F.
   manifestation.]
   1. The act of manifesting or disclosing, or the state of
      being manifested; discovery to the eye or to the
      understanding.
      [1913 Webster]

   2. That which manifests; a phenomenon which gives evidence of
      something hidden; exhibition; display; revelation; as, the
      manifestation of God's power in creation; the delayed
      manifestation of a disease.
      [1913 Webster +PJC]

            The secret manner in which acts of mercy ought to be
            performed, requires this public manifestation of
            them at the great day.                --Atterbury.
      [1913 Webster]

   3. The materialization or apparition of a spirit; -- a
      phenomenon claimed to be seen by spiritualists.
      [PJC]

WordNet (r) 3.0 (2006):

manifestation
    n 1: a clear appearance; "a manifestation of great emotion"
    2: a manifest indication of the existence or presence or nature
       of some person or thing; "a manifestation of disease"
    3: an appearance in bodily form (as of a disembodied spirit)
       [syn: materialization, materialisation, manifestation]
    4: expression without words; "tears are an expression of grief";
       "the pulse is a reflection of the heart's condition" [syn:
       expression, manifestation, reflection, reflexion]
    5: a public display of group feelings (usually of a political
       nature); "there were violent demonstrations against the war"
       [syn: demonstration, manifestation]

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "manifestation":
   announcement, apocalypse, apparition, appearance, appearing,
   arising, avatar, avowal, baring, basis for belief, blazon,
   body of evidence, bravura, brilliancy, chain of evidence,
   characterization, clue, coming, coming into being, coming-forth,
   daring, dash, data, datum, declaration, demonstration,
   denomination, denotation, designation, differentiation,
   discernibleness, disclosing, disclosure, discovering, discovery,
   display, documentation, dramatics, eclat, emergence, epiphany,
   etalage, evidence, example, exhibit, exhibition, exhibitionism,
   expose, exposition, exposure, expression, fact, facts, false front,
   fanfaronade, figure, fingering, flair, flaunt, flaunting, flourish,
   forthcoming, grounds, grounds for belief, hint, histrionics,
   identification, incarnation, indication, indicativeness, instance,
   issuance, item of evidence, laying bare, mark, material grounds,
   materialization, materializing, meaning, muniments, mute witness,
   naming, observability, occurrence, opening, outcrop, outcropping,
   pageant, pageantry, parade, patefaction, perceptibility,
   picking out, piece of evidence, pointing, pointing out,
   pointing to, premises, presentation, proof, publication,
   realization, reason to believe, relevant fact, removing the veil,
   revealing, revealment, revelation, rise, rising, seeableness,
   selection, sham, show, showing, showing forth, showing up,
   showing-off, showup, sign, signification, specification, spectacle,
   splash, splurge, staginess, stripping, suggestion, symptom,
   symptomaticness, the seen, the visible, theatrics, theophany,
   token, uncloaking, uncovering, unfolding, unfoldment, unmasking,
   unveiling, unwrapping, vaunt, visibility, visibleness, visuality,
   what is revealed