Keiren is a variant of Ciaran, an Irish name meaning little dark one.
Keiren is a variant spelling of Kieran, which comes from the Old Irish Ciarán, a diminutive of ciar, meaning dark or dark-haired — one of the most characteristically Irish of all etymologies, pragmatic in its origin but poetic in retrospect. The name was extraordinarily common in early medieval Ireland precisely because physical description was a natural source of given names, and dark-haired children in a population not uniformly so would be memorably marked. Ciarán was borne by no fewer than twenty-six saints in the Irish calendar, which speaks to how thoroughly the name was woven into the fabric of Christian Ireland.
The two most celebrated of these saints are Ciarán of Saighir, considered one of the Twelve Apostles of Ireland and said to have predated even Saint Patrick's mission, and Ciarán of Clonmacnoise, who founded one of medieval Ireland's greatest monastic centers on the Shannon River in 544 AD. Clonmacnoise became a European center of learning, producing illuminated manuscripts and scholars for centuries. The name thus carries within it the memory of Ireland's monastic golden age, when Irish monks preserved classical learning and sent missionaries across Britain and the Continent.
The spelling Keiren — shifting from the traditional Irish Ciarán or the more anglicized Kieran — reflects the name's long journey through English phonetics, where the broad Irish vowels and the fada over the á have been gradually reinterpreted. Keiren feels simultaneously traditional and contemporary, carrying its saint's legacy lightly, wearing its darkness as a kind of gentle distinction rather than a shadow.