Why abbreviating the months names?
If you were a priest living a couple of centuries ago and forced to write with a quill, trying to save your precious ink, you would do the same. Abbreviations were used everywhere possible, sometimes even a bit too much.
One of the most frequent abbreviations regards the last four months of the year:
September – October – November – December
Unlike today, however, they were never abbreviated using the month sequence number (in this case 9, 10, 11 and 12) which is a modern practice.
They were abbreviated according to their etymology, i.e to the words that compose the month names.
Here the roots of the names:
September = sette = 7
October = otto = 8
November = nove = 9
December = dieci = 10
The reason why the 12th month of the year has the number 10 in its root dates back to the Roman period, when the year started in March. But of course the way Julio Caesar was counting months is not the reason why a 19th century priest must abbreviate October putting an 8 at the beginning.
The reason lies in the way they sound, of course.
If months name in English were
Seven-ember
Eight-ember
Nine-ember
Ten-ember
You would like to abbreviate them just the way explained above, and you would not think twice in transcribing them the correct way.
This way of abbreviating months name can be found both in Italian and in Latin.
Months in Italian are:
settembre
ottobre
novembre
dicembre
Months in Latin are:
september/septembris
october/octobris
november/novembris
december/decembris
7bre = settembre (Italian) = September
8BRIS = octobris (Latin) = (of) October
9bris = novembris (Latin) = (of) November
10bre = dicembre (Italian) = December
A few more words about December.
The abbreviation 10bre is not very common. The abbreviation I found more often is Xbre, whereas X is 10 in roman figures. Why using a roman figure? Well… to abbreviate it more! In fact, 10 is made of 2 characters, whereas X is only one.
For the same reason, the roman figures are not used for the other months: they would be longer to write.
xbre = dicembre (Italian) = December