noun (n)

• the spreading of something (a belief or practice) into new regions(noun.communication)

  Synonym:
  extension
  

  source: wordnet30
• the act of producing offspring or multiplying by such production(noun.act)

  Synonym:
  generation, multiplication
  

  source: wordnet30
• the movement of a wave through a medium(noun.phenomenon)

  source: wordnet30
• The act of propagating; continuance or multiplication of the kind by generation or successive production; as, the propagation of animals or plants.(noun)

  source: webster1913