I have gone through all the Peerage and Baronage books I can find. There are five which are considered the most accurate. They list five different origins of the name. Kingship of O'Caubauin, (Ireland); Kingship of Keevan, (Ireland); from Kavanuagh, (Ireland); Northern France, meaning "the cave dweller;" and as a Sept of Clan Douglass from Kirkcudbrightshire, Scotland.
I found the earlist listings for land grants to Cavan's in Kirkcudbright. The oldest being eighty acres given to a Archibald Cavan in the 1480's.
I am trying to find a Franciscan Monk, living in the state New York, who's last name is Cavin. He claims that several Cavin's went to France in the 1220's, with about 300 other Scotsman, as an aliegence between the Kings, against England. I know the Scotish king did send about 350 warriors to France in 1221, (I think that's the correct year).
There are alot of Cavan/Caven/Cavin in Southeast Ireland. This area is very close to Southwest Scotland, Kirkcudbrightshire.
I do know the name has nothing to do with Co. Cavan, Ireland. My Father and I went there 4 years ago. Dating back to 1820, no one by the name of Cavan has ever lived/ died/married there. The word Cavan is the anglosized version of a gaelic word meaning "the hollow." The township was established in a very round valley, or hollow.
If anyone knows the "real" origin of the name, let us all know.

Jamie Cavin