Why does the ninth month come from the word seven?
For the most part, September means the end of summer, the beginning of autumn, and the start of a new school year. Out of all months, September remains the beginning of the months with less onomastically exciting names that convey nothing other than their numerical locations in the year.
In the original Roman Republic calendar, September was the seventh month, not the ninth. The Roman calendar was originally only 10 months long and included the following months- Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December.
The strangeness of calling the “ninth” month the “seventh” month didn’t seem to bother old English speakers. Had the Romans gotten their way, we might now be calling September Tiberius, or Antonius, after two Roman emperors.