Kavanagh, along with its variants Cavanagh, Cavanaugh etc., is the English version of Caomhanach, one of the very few Gaelic Irish surnames not to include "O" or "Mac". It means "follower of (St.) Caomhan", a name which is itself a diminutive of caomh, meaning "gentle" or "tender". It was first borne as a surname in the twelfth century by Donal, illegitimate son of Dermot MacMurrough, King of Leinster. He became known as "Donal Caomhánach" through having been fostered by a successor of the saint based probably at Kilcavan in Bannow parish in south Co. Wexford.
Although this Donal was the first bearer of the name, in fact the majority of the Kavanagh septs that proliferated from the fifteenth century on descend from Art MacMurrough Kavanagh, King of Leinster, who died in 1418. The territory of the Kavanaghs at this period was huge, comprising nearly all of the modern Co. Carlow, and most of north and north-west Co. Wexford. This was 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. The chiefs of the family continued to take the ruling title MacMurrough, but by the mid-sixteenth century their power was on the wane, and was decisively broken by the start of the seventeenth century, when English rule was established and north Wexford planted with English settlers.
It is not surprising, then, that Kavanaghs were prominent among the great wave of native Irish aristocrats emigrating to Europe in the wake of the final defeat of Gaelic Ireland at the end of the seventeenth century, becoming officers in the armies of Catholic France, Spain and Austria; one, Charles Kavanagh was the governor of Habsburg Prague in the mid eighteenth century
Despite their loss of power and property, the line of descent from the last duly inaugurated Chief of the Name, Brian Kavanagh, The MacMorrough, remained unbroken down to recent times. The most extraordinary among them was Arthur MacMurrough Kavanagh (1831-89), born without limbs who became the MacMorrough Kavanagh, as well as an artist, poet, adventurer, sailor, father of seven and Member of Parliament for thirteen years. Although the title became extinct in the early years of this century, a descendant of Arthur's, Andrew MacMurrough Kavanagh now lives again in the family home of Borris House.
The lion passant on the Kavanagh 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.
. The most famous modern bearer of the name was Patrick Kavanagh (1904-1967), who was the first poet of modern Ireland to give voice to the realities of life in the new state, as well as being a powerful polemicist