1. The season of the year between summer and winter, during which the weather becomes cooler and many plants become dormant, extending in the Northern Hemisphere from the autumnal equinox to the winter solstice and popularly considered to include the months of September, October, and November; fall. In the Southern Hemisphere autumn includes March, April, and May.
2. A period of maturity verging on decline.
1. Relating to or occurring in autumn: autumn foliage; autumn harvests.
2. Grown during the season of autumn: autumn crops.
[Middle English autumpne, from Old French autompne, from Latin autumnus.]
au·tum′nal (ô-tŭm′nəl) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
a. 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
b. (as modifier): autumn leaves.
2. a period of late maturity, esp one followed by a decline
[C14: from Latin autumnus, perhaps of Etruscan origin]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
au•tumn (ˈɔ təm)
1. the season between summer and winter; fall: in the Northern Hemisphere, from the September equinox to the December solstice; in the Southern Hemisphere, from the March equinox to the June solstice.
2. a time of full maturity, esp. the late stages of maturity or the early stages of decline.
[1325–75; autompne < Latin autumnus]
au•tum•nal (ɔˈtʌm nl) adj.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
The season of the year occurring between summer and winter. In the Northern Hemisphere, it extends from the autumnal equinox to the winter solstice.
The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
In British English, autumn or the autumn is the season between summer and winter.
Saturday was the first day of autumn.
The vote will take place in the autumn.
If you want to say that something happens every year during this season, you say that it happens in autumn or in the autumn.
In autumn the berries turn orange.
Birth rates are lowest in the autumn.
Don't say that something happens 'in the autumns'.
In American English, autumn is referred to as the fall.
In the fall we are going to England.
Collins COBUILD English Usage © HarperCollins Publishers 1992, 2004, 2011, 2012