The Collaborative International Dictionary of English v.0.48:

Anticlimax \An`ti*cli"max\, n. (Rhet.)
   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.

   Note: Example:

               Next comes Dalhousie, the great god of war,
               Lieutenant-colonel to the Earl of Mar.
         [1913 Webster]

WordNet (r) 3.0 (2006):

anticlimax
    n 1: a disappointing decline after a previous rise; "the
         anticlimax of a brilliant career"
    2: a change from a serious subject to a disappointing one [syn:
       anticlimax, bathos]