the third season of the year, or the season between summer and winter, often called "the fall." astronomically, it begins in the northern temperate zone at the autumnal equinox, about september 23, and ends at the winter solstice, about december 23; but in popular language, autumn, in america, comprises september, october, and november.-the harvest or fruits of autumn.-the time of maturity or decline; latter portion; third stage.