The Collaborative International Dictionary of English v.0.48:

Propagation \Prop`a*ga"tion\, n. [L. propagatio: cf. F.
   propagation.]
   [1913 Webster]
   1. The act of propagating; continuance or multiplication of
      the kind by generation or successive production; as, the
      propagation of animals or plants.
      [1913 Webster]

            There is not in nature any spontaneous generation,
            but all come by propagation.          --Ray.
      [1913 Webster]

   2. The spreading abroad, or extension, of anything;
      diffusion; dissemination; as, the propagation of sound;
      the propagation of the gospel. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

propagation
    n 1: the spreading of something (a belief or practice) into new
         regions [syn: propagation, extension]
    2: the act of producing offspring or multiplying by such
       production [syn: generation, multiplication,
       propagation]
    3: the movement of a wave through a medium

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "propagation":
   airing, attenuation, bandying, begetting, book, breeding,
   broadcast, broadcasting, bruiting, bruiting about, circulation,
   circumfusion, crossbreeding, diffraction, diffusion, dilution,
   dispensation, dispersal, dispersion, display, dissemination,
   dissipation, dissogeny, distribution, divergence, endogamy,
   engenderment, evaporation, evulgation, expansion, fragmentation,
   generation, inbreeding, issuance, issue, linebreeding,
   multiplication, outbreeding, peppering, periodical, printing,
   procreation, proliferation, promulgation, publication, publishing,
   radiation, scattering, scatterment, shotgun pattern, sowing,
   spattering, splay, spread, spreading, spreading abroad, sprinkling,
   strewing, telecasting, ventilation, volatilization, xenogamy