NOUN (3)

1. a social organization in which diversity of racial or religious or ethnic or cultural groups is tolerated;

2. the doctrine that reality consists of several basic substances or elements;

3. the practice of one person holding more than one benefice at a time;

The Collaborative International Dictionary of English v.0.48:

Pluralism \Plu"ral*ism\, n.
   1. The quality or state of being plural, or in the plural
      number.
      [1913 Webster]

   2. (Eccl.) The state of a pluralist; the holding of more than
      one ecclesiastical living at a time. [Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

pluralism
    n 1: a social organization in which diversity of racial or
         religious or ethnic or cultural groups is tolerated
    2: the doctrine that reality consists of several basic
       substances or elements [ant: monism]
    3: the practice of one person holding more than one benefice at
       a time

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "pluralism":
   Nazism, a certain number, a few, admixture, alloyage, amalgamation,
   blending, capriciousness, centralism, changeability,
   changeableness, choppiness, coalescence, collectivism, combination,
   comminglement, commingling, commixture, communism, composition,
   constitutionalism, dappleness, democratism, deviation, difference,
   differentiation, disorder, divarication, divergence,
   diversification, dualism, eclecticism, fascism, federalism,
   feudalism, feudality, fusion, governmentalism, immixture,
   imperialism, inconsistency, inconstancy, inequality, instability,
   integration, interfusion, interlarding, interlardment,
   interminglement, intermingling, intermixture, irregularity,
   jerkiness, mercuriality, merger, mingling, mixing, mixture,
   monarchism, more, motleyness, mutability, national socialism,
   neofascism, nonconformism, nonconformity, nonstandardization,
   nonuniformity, nonuniqueness, numerousness, parliamentarianism,
   parliamentarism, plurality, pluralness, political principles,
   raggedness, republicanism, royalism, several, socialism, statism,
   syncretism, unconformism, unconformity, unevenness, unorthodoxy,
   unsteadiness, variability, variation, variegation, variety,
   variousness, versatility, wavering