Diminutive of Ciar. This was the name of two Irish saints: Saint Ciarán the Elder, the patron of the Kingdom of Munster, and Saint Ciarán of Clonmacnoise, the founder of a monastery in the 6th century.
Means “ancient” in Irish. This was the name of the mythical ancestor of the Cianachta in Irish legend. Cian was also the name of a son-in-law of Brian Boru.