Kieran is the English spelling of the Irish Ciarán, from ciar, "dark", with a diminutive ending, so it means "little dark one", originally for a dark-haired child. Two early Irish saints bore the name, including Ciarán of Clonmacnoise, founder of the great monastery on the Shannon. Kieran has been in the US top 1000 all century, hovering around number 500, and climbed to number 389 in 2025, its best rank so far.