noun (n)

• (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected(noun.substance)

  Synonym:
  accelerator
  Antonym:
  anticatalyst
  

  source: wordnet30
• something that causes an important event to happen(noun.person)

  Example:
  The invasion acted as a catalyst to unite the country.
  

  source: wordnet30