When did Christmas become X-Mas?

No one knows for sure, it just happens like how people get nick names. just one day it happens, people hear it and adapt to it. The abbreviation 'Xmas' for Christmas is of Greek origin. The word for Christ in Greek is Xristos. During the 16th century, Europeans began using the first initial of Christ's name, "X" in place of the word Christ in Christmas as a shorthand form of the word. Although the early Christians understood that X stood for Christ's name, later Christians who did not understand the Greek language mistook "Xmas" as a sign of disrespect.