Merriam-Webster Collegiate Dictionary - spoiler

 noun  Date: 15th century  1.  a. one that spoils  b. one (as a political candidate) having little or no chance of winning but capable of depriving a rival of success  2.  a. a long narrow plate along the upper surface of an airplane wing that may be raised for reducing lift and increasing drag — see airplane illustration  b. an air deflector on an automobile to reduce the tendency to lift off the road at high speeds