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.
a time of full maturity, especially the late stages of full maturity or, sometimes, the early stages of decline: to be in the autumn of one's life.
(sometimes capital) Also called (esp US) fall. the season of the year between summer and winter, astronomically from the September equinox to the December solstice in the N hemisphere and from the March equinox to the June solstice in the S hemisphere (as modifier): autumn leaves
a period of late maturity, esp one followed by a decline