7ber, 8ber, 9ber, and Xber may be noted in dates in 17th and 18th century documents. These references refer to September, October, November, and December. In the modern calendar 7ber is not the 7th month, 8ber is not the 8th month, 9ber is not the 9th month, and Xber is not the 10th month. That’s a reference to their original positions. There’s more on the calendar on Wikipedia.