Although the month and date of Jesus' birth are unknown, by the early-to-mid fourth century the Western Christian Church had fixed the date of Christmas as December 25, a date that was later adopted in the East. Today, most Christians celebrate on December 25 in the Gregorian calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world. However, some Eastern Christian Churches celebrate Christmas on December 25 of the older Julian calendar, which currently corresponds to January 7 in the Gregorian calendar, the day after the Western Christian Church celebrates the Epiphany. This is not a disagreement over the date of Christmas as such, but rather a preference of which calendar should be used to determine the day that is December 25. Moreover, for Christians, the belief that God came into the world in the form of man to atone for the sins of humanity, rather than the exact birth date, is considered to be the primary purpose in celebrating Christmas.
"Christmas" is a shortened form of "Christ's mass". It is derived from the Middle EnglishCristemasse, which is from Old EnglishCrīstesmæsse, a phrase first recorded in 1038 followed by the word Cristes-messe in 1131.Crīst (genitiveCrīstes) is from Greek Khrīstos (Χριστός), a translation of HebrewMāšîaḥ (מָשִׁיחַ), "Messiah", meaning "anointed"; and mæsse is from Latin missa, the celebration of the Eucharist.
The form Christenmas was also historically used, but is now considered archaic and dialectal; it derives from Middle English Cristenmasse, literally "Christian mass".Xmas is an abbreviation of Christmas found particularly in print, based on the initial letter chi (Χ) in Greek Khrīstos (Χριστός), "Christ", though numerous style guides discourage its use; it has precedent in Middle English Χρ̄es masse (where "Χρ̄" is an abbreviation for Χριστός).
In addition to "Christmas", the holiday has been known by various other names throughout its history. The Anglo-Saxons referred to the feast as "midwinter", or, more rarely, as Nātiuiteð (from Latinnātīvitās below). "Nativity", meaning "birth", is from Latin nātīvitās. In Old English, Gēola (Yule) referred to the period corresponding to December and January, which was eventually equated with Christian Christmas. "Noel" (or "Nowel") entered English in the late 14th century and is from the Old French noël or naël, itself ultimately from the Latin nātālis (diēs) meaning "birth (day)".