What is the X in X-mas?
late 13c., "stay temporarily, reside for a time; visit;" also "reside permanently, dwell;" from Old French sojorner "stay or dwell for a time," from Vulgar Latin *subdiurnare "to spend the day" (source also of Italian soggiornare), from Latin sub- "under, until" (see sub-) + diurnare "to last long," from diurnus "of a day," from diurnum "day" (see diurnal). Modern French séjourner formed via vowel dissimilation. Related: Sojourned; sojourning.
mid-13c., "temporary stay, visit," from Anglo-French sojorn, variant of Old French sejorn, from sejorner "stay or dwell for a time" (see sojourn (v.)).