Xian (sometimes Xtian) is a common abbreviation for the word Christian. The X comes from the Greek letter Chi, the first letter of the Greek word Χριστός, Khristós, Latinized as Christus, and ultimately Anglicized as Christ. The -ian is an adjective-forming suffix originating from the equivalent Latin suffix -ianus. The abbreviation follows a pattern similar to that of Xmas. It is generally reserved for highly informal writing. The abbreviation is sometimes used in place of the male given name Christian.
The Oxford English Dictionary records Xtian as an adjective and a noun, first cited in 1845 (although Xtianity for Christianity is cited in 1634), but does not include Xian. Xian can be seen in use in The Diary of Samuel Rogers, 1634-1638, where a footnote to the printed edition states that "Throughout his diary, Rogers abbreviates 'Christ' to 'X' and the same is true of 'Christian' ('Xian'), 'Antichrist' ('AntiX') and related words."