The name Killian, an Anglicized version of the Irish name Cillian, likely originates from the Old Irish word 'cell' meaning 'church' combined with a diminutive suffix. This suggests a meaning of 'little church', possibly referring to someone who is prayerful or spiritual. The name was borne by several early Irish saints, including a 7th-century missionary to Franconia, Germany, who was martyred in Würzburg and later became the city's patron saint.