noun (n)

• an act so striking or impressive that the show must be delayed until the audience quiets down(noun.communication)

  Synonym:
  showstopper, stopper
  

  source: wordnet30
• something that is strikingly attractive or has great popular appeal(noun.attribute)

  Example:
  She has a show-stopper of a smile.
  

  Synonym:
  showstopper
  

  source: wordnet30