WordReference Random House Unabridged Dictionary of American English © 2017
Psychiatry, Psychologya period of psychological stress occurring in middle age, thought to be triggered by a physical, occupational, or domestic event, as menopause, diminution of physical prowess, job loss, or departure of children from the home.
Collins Concise English Dictionary © HarperCollins Publishers::
midlife crisis /ˈmɪdˌlaɪf/ n
- a crisis that may be experienced in middle age involving frustration, panic, and feelings of pointlessness, sometimes resulting in radical and often ill-advised changes of lifestyle