noun (n)

• passing from a more complex to a simpler biological form(noun.event)

  Synonym:
  degeneration
  

  source: wordnet30
• returning to a former state(noun.act)

  Synonym:
  regress, regression, retroversion, reversion
  

  source: wordnet30
• The act of retrograding, or going backward; retrogradation.(noun)

  source: webster1913