Pronunciation: (ô'tum),[key] —n. 1. the season between summer and winter; fall. In the Northern Hemisphere it is from the September equinox to the December solstice; in the Southern Hemisphere it is from the March equinox to the June solstice.
2. a time of full maturity, esp. the late stages of full maturity or, sometimes, the early stages of decline: to be in the autumn of one's life.