X was the designation for Christ in the greek.
Xmas" is deprecated by modern guides for writing styles. Style guides at the New York Times,[2] The Times, The Guardian, and the BBC all rule out its use, where possible.[3] Millicent Fenwick, in the 1948 Vogue's Book of Etiquette states that "'Xmas' should never be used" in greeting cards.[4] The Cambridge Guide to Australian English Usage states that the spelling should be considered informal and restricted to contexts where concision is valued, such as headlines and greeting cards.[5] The Christian Writer's Manual of Style, while acknowledging the ancient and respectful use of "Xmas" in the past, states that the spelling should never be used in formal writing.[6]