September, the ninth month, is of course named after the word for seven. I get that the Romans started their year in March so it would have been the seventh month then, but why is it still September?
Maybe we’ll find out today! But probably not because etymology is not a field of satisfying answers.
September comes from the classical Latin September, which is translated into English as… September. The first part comes from septem, which, obviously, means seven, while the -ber part is thought to be from the suffix -bris which doesn’t really have a meaning but was thought to be adjectival. Or it could be from membri, which in turn is from month [http://www.calendar-origins.com/calendar-name-origins.html]. It’s another one of those we don’t actually know things.
That’s kind of boring. Back in Old English, September used to be haerfestmonað or haligmonað, the former of which means harvest month and the latter of which means holy month. Both of which are way cooler than boring old September. Why aren’t we still using those? Stupid Romans, making everyone use their stupid calendar.
Tony Jebson’s page on the Origins of Old English