Jennilee Marigomen autumn au⋅tumn [aw-tuhm] –noun 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. a home a b c d e f g h i j k l m n o p q r s t u v w x y z ascent asleep assassin astray atmosphere autumn avert away