noun (n)

• a disappointing decline after a previous rise(noun.event)

  Example:
  The anticlimax of a brilliant career.
  

  source: wordnet30
• a change from a serious subject to a disappointing one(noun.communication)

  Synonym:
  bathos
  

  source: wordnet30
• A sentence in which the ideas fall, or become less important and striking, at the close; -- the opposite of climax. It produces a ridiculous effect.(noun)

  source: webster1913