The Collaborative International Dictionary of English v.0.48:

Diversity \Di*ver"si*ty\, n.; pl. Diversities. [F.
   diversit['e], L. diversitas, fr. diversus. See Diverse.]
   1. A state of difference; dissimilitude; unlikeness.
      [1913 Webster]

            They will prove opposite; and not resting in a bare
            diversity, rise into a contrariety.   --South.
      [1913 Webster]

   2. Multiplicity of difference; multiformity; variety.
      "Diversity of sounds." --Shak. "Diversities of opinion."
      --Secker.
      [1913 Webster]

   3. Variegation. "Bright diversities of day." --Pope.

   Syn: See Variety.
        [1913 Webster]

WordNet (r) 3.0 (2006):

diversity
    n 1: noticeable heterogeneity; "a diversity of possibilities";
         "the range and variety of his work is amazing" [syn:
         diverseness, diversity, multifariousness, variety]
    2: the condition or result of being changeable

Moby Thesaurus II by Grady Ward, 1.0:

174 Moby Thesaurus words for "diversity":
   Proteus, about-face, accommodation, adaptation, adjustment,
   agreement to disagree, alienation, allotropism, allotropy,
   alteration, amelioration, antagonism, apostasy, argumentation,
   bad copy, bad likeness, betterment, break, camouflage, change,
   change of heart, changeableness, clashing, conflict,
   constructive change, continuity, contradiction, contrariety,
   contrast, controversy, conversion, counter-culture, defection,
   degeneration, degenerative change, departure, deterioration,
   deviation, difference, disaccord, disaccordance, disagreement,
   disapprobation, disapproval, disconformity, discongruity,
   discontinuity, discord, discordance, discordancy, discrepancy,
   discreteness, disguise, disharmony, disparity, dissatisfaction,
   dissemblance, dissension, dissent, dissentience, dissidence,
   dissimilarity, dissimilation, dissimilitude, dissonance,
   distinction, distinctiveness, distinctness, disunion, disunity,
   divergence, divergency, diversification, diversion, dropping out,
   extent, faction, far cry, fitting, flip-flop, gradual change,
   her infinite variety, heterogeneity, heteromorphism, improvement,
   inaccordance, incommensurability, incomparability, incompatibility,
   incongruity, inconsistency, inconsonance, individuality,
   inequality, inharmoniousness, inharmony, irreconcilability,
   jarring, makeup, manifoldness, melioration, mere caricature,
   minority opinion, mitigation, mixture, modification, modulation,
   multifariousness, multiformity, multiplicity, negation,
   nonagreement, nonassent, nonconcurrence, nonconformity, nonconsent,
   nonuniformity, odds, omnifariousness, omniformity, opposition,
   oppugnancy, otherness, overthrow, polymorphism, poor imitation,
   qualification, radical change, range, re-creation, realignment,
   recusance, recusancy, redesign, reform, reformation, rejection,
   remaking, renewal, repudiation, repugnance, reshaping,
   restructuring, reversal, revival, revivification, revolution,
   secession, separateness, shapeshifter, shift, sudden change,
   switch, total change, transition, turn, turnabout, unconformity,
   underground, unharmoniousness, unlikeness, unorthodoxy,
   unresemblance, unsameness, unsimilarity, upheaval, variance,
   variation, variegation, variety, variousness, violent change,
   withdrawal, worsening