break down

1.  Demolish, destroy, either physically or figuratively, as in The carpenters broke down the partition between the bedrooms, or The governor's speeches broke down the teachers' opposition to school reform. [Late 1300s]
2.  Separate into constituent parts, analyze. For example, I insisted that they break down the bill into the separate charges for parts and labor, or The chemist was trying to break down the compound's molecules. [Mid-1800s]
3.  Stop functioning, cease to be effective or operable, as in The old dishwasher finally broke down. [Mid-1800s]
4.  Become distressed or upset; also, have a physical or mental collapse, as in The funeral was too much for her and she broke down in tears, or After seeing all his work come to nothing, he broke down and had to be treated by a psychiatrist. [Late 1800s]

The verb has 8 meanings:

Meaning #1: make a mathematical, chemical, or grammatical analysis of; break down into components or essential features
  Synonyms: analyze, analyse, dissect, take apart

Meaning #2: make ineffective
  Synonym: crush

Meaning #3: lose control of one's emotions
  Synonym: lose it

Meaning #4: stop operating or functioning
  Synonyms: fail, go bad, give way, die, give out, conk out, go, break

Meaning #5: separate into constituent elements or parts, as of chemical substances
  Synonyms: decompose, break up

Meaning #6: fall apart; also used metaphorically
  Synonyms: crumble, crumple, tumble, collapse

Meaning #7: cause to fall or collapse

Meaning #8: collapse due to fatigue, an illness, or a sudden attack
  Synonym: collapse