September Definition

sĕp-tĕmbər

noun

The ninth month of the year, having 30 days.

Webster's New World

Synonyms:

pronoun

The ninth month of the Gregorian calendar, following August and preceding October. Abbreviations: Sep or Sep., Sept or Sept.

Late September is a beautiful time of year.

This was one of the warmest Septembers on record.

Wiktionary

Other Word Forms of September

Singular:

September

Plural:

septembers

Late Old English, from Old French septembre, Latin september (“seventh month"), from septem (“seven"), from Proto-Indo-European *septḿ̥ (“seven"); September was the seventh month in the Roman calendar.

From Wiktionary
Middle English Septembre from Old French from Latin September the seventh month from septem seven septm̥ in Indo-European roots

From American Heritage Dictionary of the English Language, 5th Edition