What month is named after the Latin word for ten?

December gets its name from the Latin word decem (meaning ten) because it was originally the tenth month of the year in the Roman calendar, which began in March. The winter days following December were not included as part of any month. Later, the months of January and February were created out of the monthless period and added to the beginning of the calendar, but December retained its name.

The regular calendar year consisted of 304 days. The origins of the names are: Martius Mars, the god of war; Aprilis from aperiō, to open: Earth opens to receive seed; Maius from Maia, goddess of growth (maior, elder); Iunius from iunior (younger). The remaining months were named with respect to their position on the calendar: the numbers five to ten in Latin being quinque, sex, septem, octo, novem and decem, and the months were named Quintilis, Sextilis, September, October, November, and December.