Caoṁánaċ in traditional Gaelic type) is an Irish language surname first assumed by Domhnall Caomhánach, eldest son of the 12th century Diarmait Mac Murchada, king of Leinster (now Leinster, Ireland). A considerable number of anglicised variations of Caomhánach exist; some of the most common are Kavanagh, Cavanagh, Kavanaugh and Cavanaugh.
The Caomhánach family is a branch of the Mac Murchada dynasty which descended from Domhnall Caomhánach, eldest son of Diarmait, king of Leinster.
The dynasty the family descend from was known as Uí Ceinnselaig, whose territory included nearly all of County Carlow and County Wexford, with parts of Counties Wicklow and Kilkenny included. The Caomhánach family maintained control of the kingship of Leinster up until the 17th century. This claim was at times disputed and resulted in nearly consistent clashes with Anglo-Norman settlers in Ireland. The lion passant on the Caomhánach arms is a classic heraldic device associated with feudal power but unusual for a family of Gaelic extraction; it may be that it is intended to signify the centuries-long connection of the family with the kingship of Leinster.
It is referenced in a translation of the historical Annals of the Four Masters by John O’Donovan that Domhnall Caomhánach was fostered for his training and education at the monastery of Saint Cóemgen at Kilcavan in the Barony of Gorey, County Wexford. According to Irish custom, it was because of this that Domhnall assumed the name Caomhánach in the form of an descriptive byname meaning “a student or follower of Cóemgen”. Contrary to usual Irish practice, the name was adopted by his descendants as an inherited surname. In several Gaelic dictionaries, Caomhánach is also defined as “a friend, companion” and “merciful”.
Art Óg mac Murchadha Caomhánach is generally regarded as the most formidable of the later Kings of Leinster. Throughout the course of his reign, Art managed to reclaim control over much of the kingdom of Leinster. He drove the descendants of the Anglo-Norman settlers out of north Wexford and coastal Wicklow and threatened the Anglo-Irish towns of Wexford, Carlow and Dublin. The territory of the Caomhánachs at this period was huge and became known as “the Kavanagh’s country” and with good reason: Art held complete control over it, reigning for forty-two years, and even receiving dues from the English crown, the “black rent” as it was known.
Art became such a threat to the English interest in Ireland that Richard II of England made two expeditions to Ireland to bring him into submission, the latter ultimately costing Richard II his throne as he was captured and murdered upon his return to England. Art remained at large as king of Leinster until 1416 or 1417, when he was poisoned in New Ross. Although Domhnall Caomhánach was the first bearer of the name, in fact the majority of the septs that proliferated from the fifteenth century on descend from Art.