a stage in a sequence of events at which the trend of all future events, especially for better or for worse, is determined; turning point.

a condition of instability or danger, as in social, economic, political, or international affairs, leading to a decisive change.

a dramatic emotional or circumstantial upheaval in a person's life.

Medicine/Medical . the point in the course of a serious disease at which a decisive change occurs, leading either to recovery or to death. the change itself.