The Collaborative International Dictionary of English v.0.48:

Symbolism \Sym"bol*ism\, n.
   1. The act of symbolizing, or the state of being symbolized;
      as, symbolism in Christian art is the representation of
      truth, virtues, vices, etc., by emblematic colors, signs,
      and forms.
      [1913 Webster]

   2. A system of symbols or representations.
      [1913 Webster]

   3. (Chem.)
      (a) The practice of using symbols, or the system of
          notation developed thereby.
      (b) A combining together of parts or ingredients. [Obs.]
          [1913 Webster]

   4. (Theol.) The science of creeds; symbolics.
      [1913 Webster]

WordNet (r) 3.0 (2006):

symbolism
    n 1: a system of symbols and symbolic representations
    2: the practice of investing things with symbolic meaning [syn:
       symbolism, symbolization, symbolisation]
    3: an artistic movement in the late 19th century that tried to
       express abstract or mystical ideas through the symbolic use
       of images

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "symbolism":
   Sabbatarianism, allegory, allusion, anagoge, anagogics,
   anthroposophy, arcane meaning, assumption, cabala, cabalism,
   celebration, ceremonialism, charactery, cipher, coloration,
   connotation, conventional symbol, cult, cultism, cultus, emblem,
   esotericism, esoterics, esoterism, esotery, father symbol,
   fertility symbol, figuration, formalism, hint, hocus-pocus,
   iconology, ideogram, implication, implied meaning, import,
   inference, innuendo, intimation, ironic suggestion, liturgics,
   liturgiology, liturgism, logogram, logotype, love knot, meaning,
   metaphorical sense, mother symbol, mumbo jumbo, mystery, mysticism,
   mystification, nuance, occult meaning, occultism, overtone,
   phallic symbol, pictogram, presumption, presupposition, ritualism,
   rituality, ritualization, sabbatism, sacramentalism,
   sacramentarianism, solemn observance, solemnization, subsense,
   subsidiary sense, suggestion, supposition, symbol, symbolic system,
   symbolics, symbolization, symbology, tinge, token, totem,
   totem pole, touch, type, typification, undercurrent, undermeaning,
   undertone, universal symbol, yoga, yogeeism, yogism