I think it starts with a ‘c,’ and possibly ‘co.’ It’s not a common word, and as I recall looking it up, it typically doesn’t apply to anything else other than Christ’s birth (or something else about him). I read it in something a minister wrote, but now I can’t find it. Sorry for the crappy clues. [And it’s not ‘coeval’.]
Accouchement? Shot in the dark, I know.
Christmas
Not as simple as Christology (I have made the error of ignoring the obvious when searching for the right word!)
Annunciation?
A.D. is Anno Domini . There’s an equivalent which is C.E. Common Era, so it may be that someone remembered C.E. as " starts with the supposed birth of Jesus".
“The nativity” is also Christum Natum. That starts with C but its two words.
credo quia absurdum est … Well maybe ?
Here’s a list of many latin phrases, not a full dictionary of latin.
http://latin-phrases.co.uk/quotes/religious/
or wiki …
credo quia absurdum est
That’s what I was thinking. You can argue about the exact date, But Christmas is meant to remember the birth of Christ. But that’s probably not what the OP is looking for.
The wiki page for Christmas has some other words that might work for you…Cristemasse or Khrīstos, there’s a few others as well if you skim the page.
Doesn’t fit your criteria, but I think the word you’re looking for is “Incarnation”–God made flesh
corporature?
Off the wall guess: The Catholic Mass recently returned to referring in the Creed to the Father and Son as “consubstantial” in place of the phrase “one in being with.” It is not directly connected to the birth of Jesus, however.
No, that refers to the angel Gabriel coming to Mary to tell her that she was going to give birth to the Son of God.
(See, all that Catholic education DOES pay off! :D)
This is my first suggestion.
Not related to the nativity, but these are the best I could come up with that haven’t been mentioned:
Christophany: an appearance by Christ after his ascension
Chiliasm: the doctrine that Christ will rule the earth during the millennium
This might be it, at least it’s the closest so far. The same person who used it also used the word ‘aseity’ in another message, also a first-time word for me.
“incarnation” is used in other contexts (“XXX in it’s current incarnation is a piece of crap, the old one was better.”). When used in the “God made flesh” sense, it’s often the “holy incarnation”.
Enmangering.
Consutranssubtantiationnesshood