Definitions of decrease:

• noun:   the act of decreasing or reducing something
• noun:   the amount by which something decreases
• noun:   a change downward

  Example: "There was a decrease in his temperature as the fever subsided"

• noun:   a process of becoming smaller or shorter
• verb:   make smaller

  Example: "He decreased his staff"

• verb:   decrease in size, extent, or range

  Example: "The amount of homework decreased towards the end of the semester"