From Longman Dictionary of Contemporary Englishautumnau‧tumn /ˈɔːtəm $ ˈɒː-/ ●●● W3 (also fall American English) noun [countable, uncountable] TMCthe season between summer and winter, when leaves change colour and the weather becomes cooler autumn mistsGRAMMAR: Patterns with autumnin autumn/in the autumn• You use in autumn or in the autumn when saying that something happens at that time: In autumn the leaves turn red. She is planning to go back to college in the autumn.last autumn/this autumn etcDon’t use in with these words:• You say last autumn: They got married last autumn. ✗Don’t say: They got married in last autumn.• You say this autumn: The frost is early this autumn. ✗Don’t say: The frost is early in this autumn.• You say next autumn: The novel will be published next autumn. ✗Don’t say: The novel will be published in next autumn.• You say that autumn: It was very stormy that autumn. ✗Don’t say: It was very stormy in that autumn.
Examples from the Corpusautumn• Autumn began, autumn passed, and winter began, 1963 into 1964.• Only during the time of the spring and autumn equinoxes do our aquariums have a tropical day.• Shortly after Norah's departure, Louise was fitted for her autumn suits.• No recent change in status is apparent, except that some decline in autumn passage may have occurred.• In lambs, patent infections first occur in early summer, but the heaviest infections are usually seen in autumn.• Or go for lowlights in a rich autumn glow.• And in the autumn a Race Night is planned as well as a Dinner Dance.• It was not until autumn that Jennifer found herself in the city again.Origin autumn (1300-1400) Latin autumnus