Killian, as a given name, is an Anglicized version of the Irish name Cillian. One possible meaning for the name is "Church of John", cill meaning "church" and Ian being the Gaelic version of "John". The Rev. Patrick Woulfe wrote that Cillian is the 'pet' diminutive of Ceallach which means "war" or "strife".
Killian, as a surname, is found in both Ireland and Germany. Said to be derived from Saint Kilian, an Irish missionary to Germany in the 7th century, it was originally spelled Ó Cillín in Irish before being Anglicized into Killeen as well as Killian. Spelling variations for Killian include Kilian, Killion, and others.
The Killian documents controversy, referring to allegedly forged documents that were publicized during the 2004 US presidential campaign, re-opening the George W. Bush military service controversy, and raising charges of political bias or poor oversight at CBS News
Charles Killian, fictional character from the New Zealand kidult horror-fantasy series The Killian Curse
Captain Killian "Hook" Jones, a fictional character on the TV series Once Upon a Time