Abbreviations like this are very common in ancient languages (Latin). It was very common for monks who were copying manuscripts to abbreviate all kinds of things... largely because they generally already know what it said (just was we all know "xmas" means "Christmas"). We abbreviate all kinds of things these days, it's just the evolution of the language. No disrespect is meant when someone says xmas instead of Christmas.
Yes, sadly, I do have a degree in Latin and I did study paleography (ancient manuscripts).