The Collaborative International Dictionary of English v.0.48:

Proliferation \Pro*lif`er*a"tion\, n.
   [1913 Webster]
   1. (Biol.) The continuous development of cells in tissue
      formation; cell formation. --Virchow.
      [1913 Webster]

   2. (Zool.) The production of numerous zooids by budding,
      especially when buds arise from other buds in succession.
      [1913 Webster]

WordNet (r) 3.0 (2006):

proliferation
    n 1: growth by the rapid multiplication of parts
    2: a rapid increase in number (especially a rapid increase in
       the number of deadly weapons); "the proliferation of nuclear
       weapons" [ant: non-proliferation, nonproliferation]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "proliferation":
   access, accession, accretion, accrual, accruement, accumulation,
   addition, advance, aggrandizement, amplification, appreciation,
   ascent, augmentation, ballooning, begetting, bloating, boom, boost,
   breeding, broadening, buildup, burgeoning, crescendo,
   crossbreeding, development, dissogeny, edema, elevation, endogamy,
   engenderment, enlargement, escalation, expansion, extension, flood,
   fructification, gain, generation, greatening, growth, gush, hike,
   inbreeding, increase, increment, inflation, jump, leap,
   linebreeding, mounting, multiple, multiplication,
   multiplication table, multiplier, multiplying, outbreeding,
   procreation, production, productiveness, prolification,
   propagation, pullulation, raise, reproduction, rise, snowballing,
   spread, surge, swelling, tables, tumescence, up, upping, upsurge,
   upswing, uptrend, upturn, waxing, widening, xenogamy