It is an old Irish name meaning "swiftness, nimbleness." Daithi, the last pagan king of Ireland, ruled from 405 AD to 426 AD, and he had twenty-four sons. Along with Crimhthan the Great (366 A.D.) and Niall of the Nine Hostages (379 A.D.) Daithi led Irish fleets to raid the Roman Empire. He was killed by lightning in the Alps and is buried under a standing stone called "King Daithi’s Stone." As in all these matters there is debate over where the stone is located, either in County Roscommon or on the Aran Islands, off the coast of County Galway. (babynamesofireland.com)
-- Anonymous User 12/2/2007
I live in Ireland and I've only ever seen this name spelt Dáithí, not Daithí. It's pronounced DAW-hee. [noted -ed]