noun (n)

• a change for the better; progress in development(noun.event)

  Synonym:
  advance, betterment
  

  source: wordnet30
• the act of improving something(noun.act)

  Example:
  Their improvements increased the value of the property.
  

  source: wordnet30
• a condition superior to an earlier condition(noun.state)

  Example:
  The new school represents a great improvement.
  

  Synonym:
  melioration
  Antonym:
  declination, decline
  

  source: wordnet30
• The act of improving; advancement or growth; promotion in desirable qualities; progress toward what is better; melioration; as, the improvement of the mind, of land, roads, etc.(noun)

  source: webster1913