Eight

The prefix "octo-" means eight in Latin. For instance, octopus is named because of eight legs.

But the name of the month October is the 10th month in the year. So wondering thing.

This is because the origin of the name of months in Gregorian calendar. Originally, the Roman calendar includes just 10 months; Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, December.

These calendar included 304 day and there were 61 days not assigned to any month.

After some reform, adding a month and splitting it, the months became 12.

Additionally, The eighth month is named August, because of the name of Augustinus.