September Means 'Seventh.' It's the Ninth.

Septem is Latin for seven. Octo is eight. Novem is nine. Decem is ten. The English names of the last four months preserve those numerals — September, October, November, December — and all four are off by two positions.

The fault is historical. The pre-Julian Roman calendar, attributed in tradition to Romulus, had ten months and started in March. Septem-ber genuinely was the seventh month. Winter was a blank stretch with no months at all, which played havoc with any attempt to track a solar year.

Around the seventh century BC, the semi-legendary king Numa Pompilius added two new months at the end of the year — Ianuarius and Februarius — to cover the gap. For a while they stayed at the back. Roman civil reforms around 153 BC moved the start of the consular year to January 1, to align with when newly elected consuls took office. The old names kept their old numbers; they just slid.

The displacement traveled with the Roman empire, passed through Church Latin, and survived every calendar reform since. The Gregorian shift of 1582 didn't touch the month names. Even languages that don't descend from Latin — Japanese, Greek, Swahili — sometimes import the Roman names for international use, freezing the arithmetic error into the global standard.

Peter the Great tried to straighten it out in 1700, not by renaming months, but by moving Russia's new year from September to January, so the numerals were at least internally consistent. It didn't spread. September is still the ninth month. Its name will still say seven.