Source : WordNet®

show-stopper
     n 1: an act so striking or impressive that the show must be
          delayed until the audience quiets down [syn: {showstopper},
           {stopper}]
     2: something that is strikingly attractive or has great popular
        appeal; "she has a show-stopper of a smile"; "the
        brilliant orange flowers against the green foliage were a
        showstopper" [syn: {showstopper}]