Bullaun stones are boulders or rock surfaces into which one or more rounded hollows have been deliberately ground, producing shallow, bowl-like depressions that collect rainwater. They are found near early Christian sites, holy wells, and old ecclesiastical enclosures, and while their precise original function is debated, they are associated in folk tradition with cursing, healing, and the performance of rituals involving the water that gathers in the cups. The one at Killonerry belongs to this widespread but still somewhat enigmatic category of monument.

Bullaun stones as a class are thought to date from the early medieval period, though some may be older, and their connection to early monastic or devotional landscapes is well established across Irish archaeology. Killonerry itself, as a place-name, likely derives from the Irish, and the presence of a bullaun in the area suggests that it may once have formed part of a broader sacred or ecclesiastical complex, as is common for such stones in Kilkenny and elsewhere. The county has a particularly rich concentration of early medieval remains, and individual stones of this kind often survive precisely because local communities maintained a relationship with them long after their original context had faded.

Beyond the fact of its existence at Killonerry, the specific details of this stone, its dimensions, its precise location, its current condition, and any recorded local traditions attached to it, are not fully documented in available public sources at present. What can be said is that bullaun stones reward patient looking; the depressions are sometimes subtle, worn smooth by centuries of weather and, perhaps, use.