noun (n)

• someone devoted to the promotion of human welfare and to social reforms(noun.person)

  Synonym:
  do-gooder, humanitarian
  

  source: wordnet30
• a component that is added to something to improve it(noun.artifact)

  Synonym:
  add-on, addition
  

  source: wordnet30
• One who, or that which, improves.(noun)

  source: webster1913