What was the first name of Christmas?

Question

What was the first Latin word or expression used for Christmas, the Christian event in the honor of Jesus' birth? I know what to call Christmas in Latin, but it occurred to me that there is no guarantee that it wasn't called something entirely different back when the concept was first introduced in Latin. When you give attested early mentions of Christmas, please also give an estimate for time, so that it is easier to put everything on a timeline.

Answer 1

I've found mentions of Christi nativitas (Christ's birth) in Tertullian and Cyprian (late 2nd to mid-3rd century), but Christmas was not widely celebrated before the 4th century (source), and it was called Christ's dies natalis. Augustine calls it dies natalis Domini nostri Iesu Christi, or simply dies natalis Domini. Later mentions of it, e.g. by Pope Leo, are similarly worded, though sometimes omitting dies—the origin of the Italian and Portuguese Natale/Natal. See the footnotes on this and the following page for citations.

Answer 2

The earliest mention of Christmas I know is from the first line of Part 12 of the Philocalian Calendar: VIII kal. Ian. natus Christus in Betleem Iudeae. (December 25, the birth of Christ in Bethlehem of Judea.)

Because it is so common for novice Latinists to object (sometimes in comically strident terms) that natus Christus does not mean "the birth of Christ", but rather "Christ born", let me expand on this point a bit.

Latin has a strong preference for concrete terms over abstract ones, so it is pretty common to see a concrete noun with a passive participle replacing an abstract verbal noun phrase. An example can be found in Cicero's Tusculanae Disputationes. Cicero says anno ante natum Ennium to mean "in the year before the birth of Ennius". Other examples can be multiplied without looking very hard. There's the familiar example from first year textbooks, Caesar occisus cives terruit, "The murder of Caesar frightened the citizens". Urbs capta to mean "the capture of the city". Etc.

I don't claim to be widely read, but I can't recall seeing natus Christus meaning Christmas in any later texts. Christinatalis, on the other hand, seems almost ubiquitous these days.

Omnibus felicem Christinatalem hodie.