Definitions of reversal:

• noun:   a change from one state to the opposite state

  Example: "There was a reversal of autonomic function"

• noun:   a judgment by a higher court that the judgment of a lower court was incorrect and should be set aside
• noun:   a decision to reverse an earlier decision
• noun:   turning in an opposite direction or position

  Example: "The reversal of the image in the lens"

• noun:   the act of reversing the order or place of
• noun:   an unfortunate happening that hinders of impedes; something that is thwarting or frustrating
• noun:   a reversal in attitude or principle or point of view
• noun:   turning in the opposite direction