What month does Xemb. mean?

Question

I find The Parish Register of Christ Church, Middlesex County, Va., from 1653 to 1812 that reads in part:

Sarah Trigg y^e dau^tr of Daniell & Susannah Trigg bap^tz 26th of Xemb. 1686

I'm guessing that Xemb. means December, but I cannot find any source to back that up and the book has no legend for the abbreviations it uses and the adjacent entries are not chronological to give context.

Answer 1

I may be stating the obvious here, but as the etymology of this abbreviation is not covered in PolyGeo's answer:

X^ember and its associated abbreviations are using X, the Roman numeral 10, to represent the 10th month. Under the old style (Julian) calendar used in Britain and its colonies until 1752, the first month was March, making December the 10th month. Of course, the word December itself derives from the Greek with the prefix deca meaning ten.

I suspect the reason you only see December being abbreviated in this way is because to abbreviate, for example, October as XIIIober, is not really abbreviating the word at all – and required the scribe to write just as many letters.

Answer 2

To be more confident that "Xemb. means December" (which I suspect it probably does) you could look at slightly earlier entries in the same set of records for abbreviations like VIIemb., VIIIob./VIIIemb. and IXemb. (for September, October and November).

I found a Princeton University Abbreviations of the Names of the Months page that lists abbreviations for months in many languages but none of these include Roman numerals like the one you are interested in.

In the other hand FamilySearch's Latin Genealogical Word List does include:

September, 7ber, VIIber 
October, 8ber, VIIIber 
November, 9ber, IXber 
December, 10ber, Xber