1755, preceded by earlier forms such as X'temmas (1551) and Old English Χp̃es mæssa (1100), from Christmas, replacing Christ by abbreviation X, from Ancient Greek Χ (Ch, “(letter chi)”), from Χριστός (Christós, “Christ”). Surface analysis X (“Christ”) +‎ -mas (“holiday”). In popular use since late 19th century.

idk does this explaing it better