autumn

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The season of the year between summer and winter, lasting from the autumnal equinox to the winter solstice and from September to December in the Northern Hemisphere; fall.
2. n. A period of maturity verging on decline.
3. adj. Of, having to do with, occurring in, or appropriate to the season of autumn: autumn foliage; autumn harvests.
4. adj. Grown during the season of autumn: autumn crops.

Century Dictionary and Cyclopedia

1. n. The third season of the year, or the season between summer and winter: often called fall, as being the time of the falling of the leaves. Astronomically it begins at the autumnal equinox, about the 22d of September, when the sun enters Libra, and ends at the winter solstice, about the 21st of December, when the sun enters Capricorn. In popular language autumn is regarded in North America as comprising September, October, and November, but in Great Britain, August, September, and October.
2. n. Figuratively.
3. n. A period of maturity, or of incipient decay, abatement, or decline: as, the autumn of life.

Wiktionary

1. n. Traditionally the third of the four seasons, when deciduous trees lose their leaves; typically regarded as being from September 24 to December 22 in parts of the Northern Hemisphere, and the months of March, April and May in the Southern Hemisphere.
2. adj. Of or relating to autumn.

GNU Webster's 1913

1. n. 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.
2. n. The harvest or fruits of autumn.
3. n. The time of maturity or decline; latter portion; third stage.

WordNet 3.0

1. n. the season when the leaves fall from the trees