September is the month with the wrong number. Its name means 'the seventh,' yet it has been the ninth month for over two thousand years. This numerical anomaly — shared with October, November, and December — is one of the most visible fossils of the ancient Roman calendar embedded in modern timekeeping, a discrepancy so familiar that most speakers never notice it.
The Latin 'September' derives from 'septem' (seven), with the suffix '-ber' that also appears in the other numerical month names (October, November, December). The origin of this '-ber' suffix is debated: it may be related to '-bris,' an adjectival ending, or it may be an archaic formative element whose original meaning is lost. The numeral 'septem' itself descends from Proto-Indo-European *septḿ̥ (seven), one of the most stable and reliably reconstructed words in the entire proto-language, with cognates in virtually every branch of the family: Sanskrit 'saptá,' Greek 'heptá,' Gothic 'sibun,' Old Irish 'secht,' and Welsh 'saith.'
September was the seventh month in the ten-month calendar of Romulus, which ran from March (month one) through December (month ten). When King Numa Pompilius added January and February at the beginning of the year around 713 BCE, September became the ninth month, but its name was not changed. When the Roman Senate moved the official start of the civil year to January 1 in 153 BCE, the discrepancy was formalized. Despite periodic attempts at reform, the Romans' basic conservatism about calendar names
Several Roman emperors attempted to rename September. The emperor Caligula considered renaming it 'Germanicus' in honor of his father, but it was Domitian who actually did so, celebrating his Germanic military campaigns. Commodus went further, renaming it 'Amazonius' as part of his extraordinary project of renaming all twelve months after his own titles and epithets. In both cases, the renamings were immediately reversed upon the emperor's death — or, in Commodus's case, upon his assassination. The Senate's determination to restore the traditional names, even after years of forced usage, reveals just how deeply
The English word 'September' entered the language in Old English, borrowed directly from Latin. The Anglo-Saxon alternative name for this month was 'hāligmōnaþ' (holy month), which Bede explained as the month of sacred rites and offerings — probably connected to the autumn equinox and the end of the harvest season. As with all native English month names, 'hāligmōnaþ' was displaced by the Latin term.
September's cultural associations are dominated by transition. In the Northern Hemisphere, it marks the shift from summer to autumn, and the autumn equinox (around September 22–23) makes it astronomically the month when day and night are balanced. In agricultural tradition, September was the month of the grape harvest and wine-making — the Latin 'vindemia' (grape harvest) was sometimes associated with September. In the modern world, September is overwhelmingly associated with the return to school and the resumption of work after the summer holiday, giving it a dual character of fresh beginnings
The word 'September' has generated a small family of English derivatives. 'Septembrist' (a participant in the September Massacres of 1792 during the French Revolution) is the most historically specific. The musical term 'septet' and the scientific prefix 'sept-' (as in 'septennial,' occurring every seven years, and 'Septuagint,' the seventy scholars who translated the Hebrew Bible into Greek) all share the Latin root 'septem.'
The '-ember' ending shared by September, November, and December (but not October) has given rise to folk etymological connections with the word 'ember' as in 'Ember Days' — four sets of three days in the Christian liturgical calendar devoted to fasting and prayer. However, 'Ember Days' derives from Old English 'ymbren' (a circuit, a rotation), and the resemblance to the month-name suffix is purely coincidental.
Perhaps the most remarkable thing about September is the sheer persistence of its wrong number. For 2,179 years (since 153 BCE), billions of people have said 'September' — meaning 'seventh' — to refer to the ninth month, and no one has fixed it. This is a powerful testament to the inertia of language and the human willingness to let names drift free from their meanings, carrying their etymological cargo unexamined through the centuries.