Break"down` (&?;), n. 1. The act or result of breaking down, as of a carriage; downfall.

2. (a) A noisy, rapid, shuffling dance engaged in competitively by a number of persons or pairs in succession, as among the colored people of the Southern United States, and so called, perhaps, because the exercise is continued until most of those who take part in it break down. (b) Any rude, noisy dance performed by shuffling the feet, usually by one person at a time. [U.S.]

Don't clear out when the quadrilles are over, for we are going to have a breakdown to wind up with.
New Eng. Tales.

• a failure, particularly mechanical; something that has failed
       We saw a breakdown by the side of the road.
  
• a lapse of mental stability
       After so much stress, he simply suffered a breakdown and gave up.
  
• further detail or categorization
       Looking at the breakdown of the budget, I see a few items we could cut.
  
• (Chemistry:) Breaking of chemical bonds within a compound to produce simpler compounds or elements.
       synonym: degradation
  

• to fail
       I am afraid my computer will break down if I try to run it at too high a speed.
  
• to become unstable, mentally or otherwise.
  
• to decay
       Leaves and grass will break down into compost faster if you keep them moist.
  
• to give more detail
       If you don't understand, ask him to break down the numbers for you.