September (Roman month) September (Roman month) September (from Latin "septem", "seven") or mensis September was originally the seventh of ten months on the ancient Roman calendar that began with March ("mensis Martius", "Mars' month"). It had 29 days. After the reforms that resulted in a 12-month year, September became the ninth month, but retained its name. September followed what was originally Sextilis, the "sixth" month, renamed "Augustus" in honor of the first Roman emperor, and preceded October, the "eighth" month that like September retained its numerical name contrary to its position on the calendar. A day was added to September in the mid-40s
Latin Wikipedia When occasionally a term for a modern concept cannot be found, the customary practice is to do exactly what most other languages do: to borrow an international word (often from a Romance language or English). Such direct borrowing was done for the particle names and and for the unit of temperature . The word is given a Latin morphology if this can be done easily, or, if not, used unchanged in its foreign form; but many international words already have a Latin or Graeco-Latin appearance, because Greek and Latin have always served as sources of new scientific terminology. Vicipaedia made